Flexible tube for an endoscope

ABSTRACT

A flexible tube for an endoscope has an elongated tubular core body, and an outer cover which is provided over the core body. The outer cover is composed of an inner layer, an outer layer and at least one intermediate layer. In this flexible tube, any one of the layers is different from one of the other layers in its property. Further, at least one of the layers has a thickness-varying region where the thickness of the layer varies in its longitudinal direction. In addition, the inner layer of the outer cover has projections which are integrally formed on the inner layer so that the projections project into holes and/or the recesses formed on the core body. This structure makes it possible to produce a flexible tube for an endoscope that has high durability, high flexibility and high chemical resistance as well as excellent operationability.

[0001] This application is a divisional of pending U.S. patentapplication Ser. No. 09/848,301, filed May 4, 2001, the disclosure ofwhich is expressly incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a flexible tube for anendoscope.

[0004] 2. Description of the Prior Art

[0005] Generally, a flexible tube for an endoscope has a structure whichincludes a tubular core obtained by covering the outer periphery of aspiral tube with a mesh tube and an outer cover formed of a syntheticresin or the like and provided over the outer periphery of the tubularcore.

[0006] In endoscopic examination, the flexible tube for an endoscope isinserted along the body cavity to a deep part such as the stomach,duodenum, small intestine, and large intestine. In order to perform theinserting operation easily and reliably, it is necessary for theflexible tube that a push-in force applied to the proximal end (sidecloser to the operator) of the flexible tube is fully transmitted to itsdistal end. However, if bucking occurs in the flexible tube, the push-inforce can not be fully transmitted to the distal end because the push-inforce is partially absorbed by the bent part where the buckling occurs.This means that such a flexible tube for an endoscope can not achievereliable inserting operation. In order to avoid the occurrence of suchbuckling, it is necessary for the flexible tube to have sufficientflexibility so that bending is hard to occur. Further, the outer covermust be firmly attached or bonded to the tubular core since buckling isliable to occur at areas where the outer cover is peeled off from thetubular core.

[0007] Furthermore, in order to perform the inserting operationreliably, it is also necessary for the flexible tube that a rotationalforce (that is, a twist) applied to the proximal end thereof is fullytransmitted to the distal end thereof. In other word, a flexible tubefor an endoscope is also required to have satisfactory rotationalfollowability.

[0008] Moreover, a flexible tube for an endoscope is also required tohave a relatively high stiffness on the proximal end side (side closerto the operator) and have a flexibility on the distal end side from theviewpoint of the operability and safety of insertion and reduction inthe burden on the patient.

[0009] Up to now, there are known several flexible tubes for anendoscope which aim to improve the insertion operability in view of theproblems described above. One of such flexible tubes is disclosed inJapanese Laid-open Patent Applications No. Hei 5-50287, in which anouter cover of a flexible tube for an endoscope is constructed from adouble layer structure comprised of an outer layer made of a materialhaving good elasticity and an inner layer made of a material having goodresiliency, thereby improving resiliency of the flexible tube as awhole. Other example of such flexible tube is disclosed in JapanesePatent No. 2641789, in which a distal end side of the flexible tube ismade of a soft elastomer and a proximal end side thereof is made of ahard elastomer so that the stiffness varies from the distal end sidetoward the proximal end side.

[0010] However, in these prior arts described in the above, the bondingforce between the outer cover and the core has been left out ofconsideration, so that there is a case that the outer cover is peeledoff from the core after repeated use, thus leading to the deteriorationin flexibility and resistance to buckling of the flexible tube. Inshort, there is a problem in the durability of the flexible tube for anendoscope.

[0011] Furthermore, although an endoscope must be cleaned anddisinfected every time when it is used, in the above prior arts noconsideration is given to the chemical resistance of the outer covers.Consequently, in these prior arts, deterioration proceeds during therepeated disinfections, which results in possibility of generation offine cracks or the like and peeling off of the outer cover from thecore.

SUMMARY OF THE INVENTION

[0012] In view of the problems in the prior art described in the above,it is the object of the present invention to provide a flexible tube foran endoscope that possesses various kinds of performances required for aflexible tube for an endoscope, in particular to provide a flexible tubefor an endoscope excellent in the operability of insertion, resistanceto chemicals and durability.

[0013] In order to achieve the above object, the present invention isdirected to a flexible tube for an endoscope, comprising:

[0014] an elongated tubular core body; and

[0015] an outer cover which is provided over the core body, the outercover having a portion which is formed into a laminate structurecomposed of at least three layers.

[0016] In this invention, it is preferred that the layers of thelaminate structure include an inner layer, an outer layer and at leastone intermediate layer formed between the inner layer and the outerlayer.

[0017] Further, in this invention, it is also preferred that the corebody has a plurality of holes and/or a plurality of recesses. In thiscase, it Is preferred that the core body includes: a coil that is formedby winding a band-shaped material into a spiral form; and a reticulartube that is formed by weaving a plurality of fine wires together, thereticular tube being provided over the coil. Further, it is alsopreferred that the inner layer of the outer cover has projections whichare integrally formed on the inner layer so that the projections projectinto the holes and/or the recesses.

[0018] Furthermore, in this invention, it is also preferred that atleast one of the fine wires forming the reticular tube is coated with asynthetic resin so that a coating of the synthetic resin is provided onthe fine wire, in which at least a part of the coating is fused with andbonded to the inner layer of the outer cover.

[0019] Moreover, in this invention, it is also preferred that the innerlayer of the outer cover contains a material having a compatibility withthe synthetic resin of the coating.

[0020] Further, in this invention, it is also preferred that the portionof the laminate structure of the outer cover has a substantially uniformthickness over its entire region.

[0021] Furthermore, in this invention, it is also preferred that any oneof the inner, outer and intermediate layers is different from one of theother layers in its physical property and/or chemical property.

[0022] Moreover, in this invention, it is also preferred that any one ofthe inner, outer and intermediate layers is different from one of theother layers in its hardness.

[0023] Moreover, in this invention, it is also preferred that the outerlayer of the outer cover contains a material having resistance tochemical.

[0024] Moreover, in this invention, it is also preferred that theintermediate layer of the outer cover is formed of a material havinghigher elasticity than that of the outer layer.

[0025] Moreover, in this invention, it is also preferred that the outerlayer of the outer cover is formed of a material having higher hardnessthan that of any one of the inner and intermediate layers.

[0026] Moreover, in this invention, it is also preferred that at least apart of the outer layer of the outer cover has higher hardness than thatof any of the inner and intermediate layers.

[0027] Moreover, in this invention, it is also preferred that theintermediate layer of the outer cover is formed so as to function ascushioning means between the inner layer and the outer layer.

[0028] Moreover, in this invention, it is also preferred that at leastone of the inner, outer and intermediate layers of the outer cover isformed of a material that contains at least one selected from the groupconsisting of polyurethane-based elastomer, polyester-based elastomer,polyolefine-based elastomer, polystyrene-based elastomer,polyamide-based elastomer, fluorine-based elastomer, and fluororubber.

[0029] Moreover, in this invention, it is also preferred that each ofthe inner, outer and intermediate layers of the outer cover is formed ofa material that contains at least one selected from the group consistingof polyurethane-based elastomer, polyester-based elastomer,polyolefine-based elastomer, polystyrene-based elastomer,polyamide-based elastomer, fluorine-based elastomer, and fluororubber.

[0030] Further, in this invention, it is also preferred that the outercover is provided over the core body through an extrusion moldingprocess.

[0031] Furthermore, in this invention, it is also preferred that theflexible tube has tip and base ends, and flexibility of the flexibletube increases in a gradual or stepwise manner along the direction fromthe base end toward the tip end.

[0032] Moreover, in this invention, it is also preferred that any one ofthe layers constituting the portion of the laminate structure of theouter cover is different from one of the other layers in its physicalproperty and/or chemical property.

[0033] Moreover, in this invention, it is also preferred that any one oflayers constituting the laminate structure of the outer cover isdifferent from one of the other layers in hardness.

[0034] Moreover, in this invention, it is also preferred that at leastone of the layers constituting the portion of the laminate structure hasa thickness-varying region where the thickness of the layer varies inits longitudinal direction.

[0035] In this case, it is preferred that the thickness-varying regionextends substantially over an entire region of the layer, and within thethickness-varying region the thickness of the layer varies in itslongitudinal direction in a gradual or stepwise manner.

[0036] Further, it is also preferred that the layer with thethickness-varying region has at least one uniform thickness region whichis formed so as to adjoin the thickness-varying region.

[0037] Furthermore, it is also preferred that the layer having thethickness-varying region is formed of a material that is different frommaterials constituting the other layers in its hardness.

[0038] Moreover, it is also preferred that each of at least two of thelayers constituting the portion of the laminate structure has athickness-varying region where the thickness of the layer varies in itslongitudinal direction.

[0039] Moreover, it is also preferred that the outer cover is providedover the core body through an extrusion molding process. In this case,it is preferred that in the extrusion molding process a constituentmaterial for each of the layers is fed at a predetermined feeding ratewhile the core body is fed at a predetermined feeding speed, in whichthe thickness of the layer having the thickness-varying region iscontrolled by adjusting the feeding rate of the material for the layerduring the extrusion molding process and/or adjusting the feeding speedof the core body during the extrusion molding process.

[0040] Further, in this invention, it is preferred that at least one ofthe layers constituting the portion of the laminate structure has atleast two regions and at least one boundary part along its longitudinaldirection, and one of the regions is contiguous to the other regionthrough the boundary part, in which one of the regions is different fromthe other regions adjacent thereto in its physical property and/orchemical property.

[0041] In this case, it is preferred that one of the regions is formedof a material which is different from that forming the other regionadjacent thereto.

[0042] Further, it is also preferred that each of at least two of thelayers constituting the portion of the laminate structure has at leasttwo regions and at least one boundary part along its longitudinaldirection, and one of the regions is contiguous to the other regionthrough the boundary part, in which one of the regions is different fromthe other region adjacent thereto in its physical property and/orchemical property. In this case, it is preferred that the outer cover isformed such that the boundary part of one layer is not located above orbelow the boundary part of the other layer in its thickness direction.

[0043] Furthermore, it is also preferred that the boundary part isformed as a property-varying part within which the physical propertyand/or the chemical property of the layer gradually vary in itslongitudinal direction. In this case, the boundary part is formed of amixture of a material constituting one of the regions and a materialconstituting the other region.

[0044] Moreover, it is also preferred that the layer having the boundarypart is formed such that the physical property and/or the chemicalproperty within the boundary part vary in its longitudinal direction ina substantially stepwise manner.

[0045] Moreover, it is also preferred that in the layer having the atleast two regions, one of the regions is different from the other regionadjacent thereto in its hardness.

[0046] Moreover, it is also preferred that the flexible tube has tip andbase ends, and flexibility of the flexible tube increases in a gradualor stepwise manner along the direction from the base end to the tip end.

[0047] These and other objects, structures and advantages of the presentinvention will be apparent more clearly from the following descriptionof the invention based on the examples.

BRIEF DESCRIPTION OF THE DRAWINGS

[0048]FIG. 1 shows an overall structure of an endoscope having a firstembodiment of a flexible tube according to the present invention;

[0049]FIG. 2 is a sectional view which shows a part of the flexible tubein FIG. 1;

[0050]FIG. 3 is a sectional view which shows a part of a secondembodiment of the flexible tube according to the present invention;

[0051]FIG. 4 is a sectional view which shows a part of a thirdembodiment of the flexible tube according to the present invention;

[0052]FIG. 5 is a sectional view which shows a part of a fourthembodiment of the flexible tube according to the present invention;

[0053]FIG. 6 is a sectional view which shows a part of a fifthembodiment of the flexible tube according to the present invention;

[0054]FIG. 7 is a sectional view which shows a part of a sixthembodiment of the flexible tube according to the present invention;

[0055]FIG. 8 is a sectional view which shows a part of a seventhembodiment of the flexible tube according to the present invention;

[0056]FIG. 9 is a sectional view which shows a part of an eighthembodiment of the flexible tube according to the present invention;

[0057]FIG. 10 is a sectional view which shows a part of a ninthembodiment of the flexible tube according to the present invention;

[0058]FIG. 11 is a sectional view which shows a part of a tenthembodiment of the flexible tube according to the present invention;

[0059]FIG. 12 is a sectional view which shows a part of an eleventhembodiment of the flexible tube according to the present invention;

[0060]FIG. 13 is an illustration which shows a state where an flexibletube is divided into eight sections;

[0061]FIG. 14 is an illustration which shows a state where an flexibletube is divided into ninth sections; and

[0062]FIG. 15 is an illustration which shows a state where the bendingstiffness in one of the sections shown in FIG. 13 or 14 is measured.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0063] Hereinafter, detailed description of the preferred embodiments ofa flexible tube for an endoscope according to the present invention willbe given with reference to the appended drawings.

I. First Embodiment (Flexible Tube 1A)

[0064] (I-1) Overall-Structure of Electronic Endoscope

[0065] First, a first embodiment of the flexible tube for an endoscopewill be described-with reference to FIGS. 1 and 2. FIG. 1 shows anoverall structure of an electronic endoscope 10 (electronic scope)having a flexible tube 1A according to the present invention. FIG. 2 isa sectional view which shows a part of the flexible tube 1A of theelectronic endoscope 10 in FIG. 1. In FIG. 2, the right-hand sidecorresponds to the base side (i.e., side closer to an operator), and theleft-hand side corresponds to the tip side of the electronic endoscope10.

[0066] In the following, the upper side and the lower side in FIG. 1will be referred to as “base” and “tip,” respectively. Further, theelectronic endoscope will be referred to simply as an “endoscope.”Furthermore, the flexible tube for an endoscope will be referred tosimply as a “flexible tube.”

[0067] As shown in FIG. 1, the endoscope 10 has an elongated flexibletube (insertion section) 1A designed to be inserted into a body cavityof a living body; a bendable tube 5 provided on a tip end 12 of theflexible tube 1A; an operating section 6 provided on a base end 11 ofthe flexible tube 1A, which is gripped by an operator during anendoscopic examination to manipulate the endoscope 10; a light guideflexible tube 7 connected at one end thereof to the operating section 6;and a plug 8 provided on the other end of the light guide flexible tube7.

[0068] On the side faces of the operating section 6, there are providedoperating knobs 61 and 62. When changing the direction of the bendabletube 5 during the endoscopic examination, the operator turns each of theoperating knobs 61 and 62 to pull appropriately wires (not shown)arranged in the flexible tube 1A. In this way, the bendable tube 5 isbent to a desired direction.

[0069] The endoscope 10 has an imaging element (CCD) for taking an imageof an observation area, which is provided at the tip end of the bendabletube 5. Further, the endoscope 10 has a connector 82 provided on one endof the plug 8. The connector 82 is connected to a light source devicewhich is connected to a monitor (not shown) via a cable.

[0070] In the endoscope 10, the reflected light (which forms an image ofthe observation area) from the observation area is received by theimaging element. Then, the imaging element outputs an image signalcorresponding to the image formed on the imaging element by thereflected light. The image signal is transmitted to the plug 8 via animage signal cable (not shown in the drawing) which extends inside thebendable tube 5, the flexible tube 1A, the operating section 6 and thelight guide flexible tube 7. Then, in the light source device, the imagesignal is subjected to predetermined processing (such as signalprocessing, image processing, and the like), and then the processedsignal is sent to the monitor. In this way, an image (electronic image)taken by the imaging element is displayed on the screen of the monitor.

[0071] In the above, the description was given for the case where aflexible tube for an endoscope according to the present invention isapplied to an electronic endoscope (electronic type endoscope). However,it is to be noted that a flexible tube of this invention may also beapplied to a fiberscope (optical type endoscope).

[0072] As shown in FIG. 2, the flexible tube 1A has a core body(structural body) 2 and an outer cover 3 that covers an outer peripheryof the core body 2. Further, inside the flexible tube 1A, there isformed a hollow space 24 through which internal elements (such asoptical fibers, cables, operation wires, tubular elements, and the like)can be passed.

[0073] The core body 2 acts as a reinforcing member for reinforcing theflexible tube 1A, and also acts as a protecting member for protectingthe internal elements described above. This core body 2 is constructedfrom a coil 21 and a reticular tube 22 which covers the outer peripheryof the coil 21, so that the core body 2 has an elongated tubular shape.By constructing the core body 2 using the coil 21 and the reticular tube22, it becomes possible to give the flexible tube 1 torque transmissionability, tracking ability to a body cavity (i.e., bendability), andsufficient mechanical strength.

[0074] The coil 21 is formed from a flat metal band. Specifically, thiscoil 21 is formed by winding the metal band into a spiral form so as tohave a uniform diameter with a gap 25 between the adjacent windings.Preferred examples of materials which may be used for the metal bandinclude stainless steel, copper alloys, and the like.

[0075] The reticular tube 22 is formed by weaving a plurality of bundlesof fine metal wires 23 in a lattice manner so as to have spaces 26 therebetween as shown in FIG. 2. Each of the bundles is formed by arranging aplurality of fine wires side by side. This reticular tube 22 may beformed from nonmetal fibers. Preferred examples of materials which maybe used for the fine metal wires 23 include stainless steel, copperalloys and the like. In this invention, it is preferred that at leastone of the fine wires (or fibers) constituting the reticular tube 22 iscoated with a synthetic resin so that a coating of the synthetic resinis provided thereon.

[0076] On the outer periphery of the reticular tube 22, each of thespaces 26 of the reticular tube 22 forms either a recess or hole of thecore body 2 depending on its location with respect to the coil 21.Specifically, as shown in FIG. 2, some of the spaces 26 located on themetal band of the coil 21 form recesses of the core body 2, while theother spaces 26 located on the gaps 25 between the adjacent windingsform holes of the core body 2. As a result of the structure describedabove, the core body 2 has a plurality of recesses and holes.

[0077] The outer periphery of the core body 2 is covered with the outercover 3. This outer cover 3 or a portion of the outer cover 3 is formedinto a laminate structure which is composed of inner, outer andintermediate layers 31-33.

[0078] As will be described below, one of the inner, outer andintermediate layers 31-33 of the outer cover 3 is formed of a materialwhich is different from a material constituting one of the other layersin its physical property or chemical property. Examples of such physicalproperty include stiffness, flexibility, hardness, elongation rate,tensile strength, shearing strength, bending strength and the like.Further, examples of such chemical property include chemical resistance,weather resistance and the like.

[0079] (I-2) Inner Layer of Outer Cover

[0080] The inner layer 31 of the outer cover 3 is formed on theinnermost side of the outer cover 3, and it adheres to the core body 2.Physical property of the inner layer 31 is substantially homogeneousover its entire region.

[0081] On the inner peripheral surface of the inner layer 31, as shownin FIG. 2, there are integrally formed a plurality of projections(anchoring projections) 4. Respective projections 4 project into spaces26 of the core body 2 (i.e., holes and recesses of the core body 2). Asshown in FIG. 2, in the recesses (spaces 26) of the core body 2, each ofthe projections 4 extends to the outer periphery of the coil 21.Further, in the holes (spaces 26) of the core body 2, each of theprojections 4 extends into the gap 25 of the coil 21.

[0082] In this invention, it is preferable that the inner layer 31 ismade of a material by which formation of the projections 4 can becontrolled appropriately, so that appropriate number of projections 4having appropriate size and shape can be integrally formed on the innerlayer 31 as shown in FIG. 2.

[0083] By forming the projections 4 as described above, engagementsbetween the projections 4 and the recesses of the core body 2 andbetween the projections 4 and the holes of the core body 2 are achieved,and therefore the outer cover 3 is firmly fixed with respect to the corebody 2 by anchoring effect given by the engagements. Such anchoringeffect enables the outer cover 3 to expand and contract sufficiently inconformity with the bending of the core body 2. Further, due to theanchoring effect, it is possible to maintain a state that the outercover 3 adheres to the core body 2 even when the flexible tube 1A isbended. Therefore, by forming the flexible tube in this way, it ispossible to give high flexibility to the flexible tube.

[0084] Further, the bonding strength between the outer cover 3 and thereticular tube 22 is enhanced by the formation of the projections 4, sothat the peeling off of the outer cover 3 from the reticular tube 22 isprevented even after repeated use of the endoscope. This means that theflexible tube 1A of this invention can maintain high flexibility evenafter the endoscope is repeatedly used, that is, the flexible tube hasexcellent durability.

[0085] Further, when the coating of the synthetic resin is given to atleast one of the fine wires 23 forming the reticular tube 22 asdescribed above, at least a part of the applied coating (syntheticresin) is fused with and is bonded to the inner layer 31, therebyproviding strong bonding therebetween. In this case, in order to enhancethe boding strength between the fine wires 23 and the inner layer 31, itis preferable that the inner layer 31 of the outer cover 3 contains amaterial that has a compatibility with the synthetic resin of thecoating.

[0086] By using the reticular tube 22 formed from the fine wires withthe coating of the synthetic resin as described above, a higher adhesionbetween the outer cover 3 and the core body 2 is realized. Therefore, byproviding the outer cover 3 on the core body 2 having the reticular tube22 with the coating of the synthetic resin and by forming theprojections 4 on the inner layer 31 as described above, it becomespossible to obtain a flexible tube having high flexibility and highdurability. In this connection, it is to be noted this excellent abilityis given by the effect of the coating of the synthetic resin provided onthe fine wire(s) as well as the effect of the projections 4 describedabove.

[0087] In this invention, a constituent material for the inner layer 31is not particularly limited. Examples of such material include variousresins having elasticity such as polyvinyl chloride, polyolefine (e.g.,polyethylene, polypropylene, ethylene-vinylacetate copolymer and thelike), polyamide, polyester (e.g., polyethylene terephthalate (PET),polybutylene terephthalate and the like), polyurethane, polystyreneresin, fluoro-based resin (e.g., polytetrafluoroethylene,ethylene-tetrafluoroethylene copolymer and the like), polyimide, and thelike; and various elastomers such as polyurethane-based elastomer,polyester-based elastomer, polyolefine-based elastomer, polyamide-basedelastomer, polystyrene-based elastomer, fluorine-based elastomer,silicone rubber, fluororubber, latex rubber, and the like. These can beused alone or as a mixture of two or more thereof. In this invention, amaterial containing at least one of polyurethane-based elastomer,polyolefin-based elastomer, and polyester-based elastomer is preferablyused to form the inner layer 31, since they can be easily formed intothe inner layer with the projections 4 as shown in FIG. 2.

[0088] The average thickness of the inner layer 31 (excluding theportions of the projections 4) is not particularly limited, but thethickness is preferably in the range of 0.05 to 0.8 mm, and morepreferably in the range of 0.05 to 0.4 mm.

[0089] (I-3) Outer Layer of Outer Cover

[0090] The outer layer 32 is formed on the outermost side of the outercover 3, and has almost homogeneous physical properties over its entireregion. In this invention, it is preferable that the outer layer 32 isformed of a material having a resistance to chemicals. By using such amaterial, it is possible to suppress the degradation of the outer cover3 due to repeated cleaning and disinfection. Further, it is alsopossible to suppress deterioration in flexibility caused by thehardening of the outer cover due to repeated cleaning and disinfection.In addition, it is also possible to prevent peeling off of the outercover 3 from the reticular tube 22 due to cracks or the like caused byrepeated cleaning and disinfection.

[0091] The outer layer 32 is formed so as to have a relatively highhardness. This prevents the generation of scratches that are liable toproduce cracks or the like on the surface of the outer cover 3. In thisinvention, it is preferable that the outer layer 32 of the outer cover33 has higher hardness than that of any one of the inner andintermediate layers 31 and 33 in part or over its entire region.

[0092] In this invention, a constituent material for the outer layer 32is not particularly limited. Examples of such material include variousresins having elasticity such as polyvinyl chloride, polyolefine (e.g.,polyethylene, polypropylene, ethylene-vinylacetate copolymer and thelike), polyamide, polyester (e.g., polyethylene terephthalate (PET),polybutylene terephthalate and the like), polyurethane, polystyreneresin, fluoro-based resin (e.g., polytetrafluoroethylene,ethylene-tetrafluoroethylene copolymer and the like), polyimide, and thelike; and various elastomers such as polyurethane-based elastomer,polyester-based elastomer, polyolefine-based elastomer, polyamide-basedelastomer, polystyrene-based elastomer, fluorine-based elastomer,silicone rubber, fluororubber, latex rubber, and the like. These can beused alone or as a mixture of two or more thereof. In this invention, amaterial containing at least one of polyolefine (e.g.,ethylene-vinylacetate copolymer and the like), fluoro-based resin (e.g.,polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer and thelike), polyester-based elastomer, polyolefine-based elastomer,fluorine-based elastomer, silicone rubber and fluororubber is preferablyused to form the outer layer 32, since they have high resistance tochemical.

[0093] The thickness of the outer layer 32 is not particularly limited,but the thickness is preferably in the range of 0.05 to 0.8 mm, and morepreferably in the range of 0.05 to 0.4 mm.

[0094] (I-4) Intermediate Layer of Outer Cover

[0095] In this invention, it is preferable that the intermediate layer33 has a higher elasticity than that of the outer layer 32, and morepreferably the intermediate layer 33 has a higher elasticity than thatof any one of the inner and outer layers 31 and 32. With thisarrangement, the intermediate layer 33 functions as a cushioning layer(cushioning means) between the inner layer 31 and the outer layer 32.(In the following, such a function of the intermediate layer 33 isreferred to as “cushioning function.”) Accordingly, by forming theintermediate layer 33 as described above, it is possible to give higherflexibility to the flexible tube.

[0096] Hereinafter, the cushioning function of the intermediate layer 33is described in more detail. When the flexible tube 1A is bent by anexternal force, the high elastic force is generated in the bentintermediate layer 33 through the deformation thereof. The generatedelastic force is transmitted effectively to the inner layer 31 and theouter layer 32, respectively, since the intermediate layer 33 issandwiched between the inner layer 31 and the outer layer 32 each ofwhich has relatively low elasticity. When the external force has beenremoved, the bent flexible tube 1A is restored to its original shape bythe high elastic force generated in the bent intermediate layer 33. Inthis connection, it is to be noted that the restoration of the flexibletube into its original shape is achieved by the cushioning function ofthe intermediate layer 33, and that such a cushioning function gives theflexible tube high flexibility.

[0097] In this invention, a constituent material for the intermediatelayer 33 is not particularly limited. Examples of such material includevarious resins having elasticity such as polyvinyl chloride, polyolefine(e.g., polyethylene, polypropylene, ethylene-vinylacetate copolymer),polyamide, polyester (e.g., polyethylene terephthalate (PET),polybutylene terephthalate), polyurethane, polystyrene resin,fluoro-based resin (e.g., polytetrafluoroethylene,ethylene-tetrafluoroethylene copolymer), polyimide, and the like; andvarious elastomers such as polyurethane-based elastomer, polyester-basedelastomer, polyolefine-based elastomer, polyamide-based elastomer,polystyrene-based elastomer, fluorine-based elastomer, silicone rubber,fluororubber, latex rubber, and the like. These can be used alone or asa mixture of two or more thereof. In this invention, a materialcontaining at least one of low hardness polyurethane-based elastomer,low hardness polyolefin-based elastomer, and low hardnesspolyester-based elastomer is preferably used to form the intermediatelayer 33, since such elastomers have high elasticity.

[0098] Although the intermediate layer 33 in this embodiment is given asingle layer structure, it may be given a structure of two or morelayers.

[0099] The average thickness of the intermediate layer 33 is notparticularly limited, but the average thickness is preferably in therange of 0.05 to 0.8 mm, and more preferably in the range of 0.05 to 0.4mm.

[0100] (I-5) Outer Cover Having the Layers

[0101] In this invention, the average thickness of the outer cover 3(excluding the portions of the projections 4) is not particularlylimited, as long as the outer cover 3 can protect the core body 2 andthe internal elements arranged in the core body 2 from a fluid (e.g.,body fluid) and it does not impair the bendability of the flexible tube.However, the average thickness of the outer cover 3 (excluding theportions of the projections 4) is preferably in the range of 0.15 to 0.9mm, and more preferably in the range of 0.3 to 0.8 mm.

[0102] In addition, it is preferable that the outer cover 3 (excludingthe portions of the projections 4) has a substantially uniform-thicknessover its entire region. With this arrangement, it is possible to producea flexible tube having a substantially uniform diameter over its entireregion. When an endoscope having a flexible tube with such an outercover is used in an endoscopic examination, it is possible for anoperator to easily and smoothly insert the insertion section (flexibletube) of the endoscope into a body cavity of a patient, thus making itpossible to reduce the burden on the patient during the endoscopicexamination.

[0103] (I-6) Manufacturing Method of Flexible Tube

[0104] A method of manufacturing a flexible tube for an endoscope asdescribed in the above is not particularly limited, but it is preferablethat the flexible tube of this invention is manufactured by extrusionmolding. When such extrusion molding is performed using an extrusionmolding machine equipped with a plurality of extrusion ports, it ispossible to extrude the inner, outer and intermediate layers 31-33simultaneously so that the core body 2 is covered with the outer cover 3having the laminate structure composed of these layers. In thisextrusion molding, it is preferable to adjust the feeding amount (i.e.,feeding amount per unit time) of constituent material for each layerfrom each extrusion port while adjusting the feeding speed of the corebody 2. This method makes it is possible to control properly thethickness, shape and property of each layer.

[0105] The temperature of the material when performing the extrusionmolding is not particularly limited, but the temperature is preferablyabout 130 to 220° C., and more preferably about 165 to 205° C. Withinsuch a range, the material has an excellent moldability. Therefore, byperforming the extrusion molding using the material whose temperature iswithin the range described above, it becomes possible to improveuniformity of the thickness of the outer cover 3 provided on the corebody 2.

II. EXAMPLES OF FIRST EMBODIMENT

[0106] Next, specific examples of the first embodiment of the presentinvention will be described below.

[0107] 1. Preparation of Flexible Tube for an Endoscope

Example 1a

[0108] First, a coil 21 having an outer diameter of 9.9 mm and an innerdiameter of 9.6 mm was prepared by winding a band-shaped stainless steelmaterial having a width of 3 mm. Next, stainless steel fine wires 23 atleast one of which had been given a coating of a polyamide resin andeach of which had a diameter of 0.1 mm were prepared, and then usingthese fine wires a plurality of bundles of ten fine wires were prepared.These bundles of the ten fine wires 23 were woven together in a latticemanner to obtain a reticular tube 22. Then, the obtained reticular tube22 was provided on the prepared coil 21 so that the outer periphery ofthe coil 21 was covered with the reticular tube 22. In this way, a corebody 2 was prepared.

[0109] Next, using an extrusion-molding machine, an outer cover 3composed of inner, outer and intermediate layers 31-33 was provided onthe outer periphery of the core body 2 so that the core body 2 wascovered with the outer cover 3. In this way, a flexible tube for anendoscope with a length of 1.6 m was prepared. In this connection, it isto be noted that the length of 1.6 m means the length of an available(effective) portion of the flexible tube that can be used for a flexibletube for an endoscope, that is the length of 1.6 m means an available(effective) length of the flexible tube. Therefore, the actuallyprepared flexible tube had a length more than 1.6 m by includingadditional portions at the both ends of the available portion of theflexible tube. In this regard, however, it goes without saying that theavailable length is not limited to 1.6 m mentioned above.

[0110] A constituent material used for each of the layers in thisExample is shown in the attached Table 1. In addition, the thickness ofeach of the layers is also shown in Table 1.

Example 1b

[0111] A flexible tube for an endoscope was prepared in the same manneras in Example 1a except that the thickness of the inner layer 31 waschanged as shown in the attached Table 1.

Example 1c

[0112] A flexible tube for an endoscope was prepared in the same manneras in Example 1a except that the thickness of the intermediate layer 33was changed as shown in the attached Table 1.

Example 1d

[0113] A flexible tube for an endoscope was prepared in the same manneras in Example 1a except that the thickness of the outer layer 32 and thematerial for the outer layer 32 were changed as shown in the attachedTable 1.

Example 1e

[0114] A flexible tube for an endoscope was prepared in the same manneras in Example 1a except that the material for the outer layer 32 waschanged as shown in the attached Table 1.

Comparative Example 1a

[0115] A core body 2 was prepared in the same manner as in Example 1a.Then, using an extrusion-molding machine, an outer cover 3 composed ofinner and outer layers 31 and 32 was provided on the outer periphery ofthe core body 2 so that the core body 2 was covered with the outer cover3. In this way, a flexible tube for an endoscope with a length of 1.6 mwas prepared. A constituent material for each layer of the outer cover 3and the thickness of each layer are shown in the attached Table 1.

Comparative Example 1b

[0116] A flexible tube for an endoscope was prepared in the same manneras in Comparative Example 1a except that the material for the outerlayer 32 was changed as shown in the attached Table 1.

Comparative Example 1c

[0117] A flexible tube for an endoscope was prepared in the same manneras in Example 1a except that the thickness of each of inner and outerlayers 31 and 32 and the material for each of the inner and outer layers31 and 32 were changed as shown in the attached Table 1.

Comparative Example 1d

[0118] A flexible tube for an endoscope was prepared in the same manneras in Example 1a except that the material for each of inner and outerlayers 31 and 32 was changed as shown in the attached Table 1.

[0119] 2. Observation of the Prepared Flexible Tubes

[0120] An observation of the cross-section of the outer cover wascarried out for each of the flexible tubes of Examples 1a-1e andComparative Examples 1a-1d. Through the observation, formation ofprojections 4 as shown in FIG. 2 was observed in each of the flexibletubes of Examples 1a-1e and Comparative Examples 1a, 1b and 1d, but noformation of projections 4 was observed in the flexible tube ofComparative Example 1c.

[0121] 3. Evaluation of Flexible Tube

[0122] (3-1) Chemical Resistance Test

[0123] A chemical resistance test was carried out for each of theflexible tubes of Example 1a-1e and Comparative Example 1a-1d. In thistest, 100 L of 10% aqueous solution of iodine held at 25° C. wasprepared first, and then each of the prepared flexible tubes wasimmersed in the aqueous solution for 200 hours. Then, the condition ofeach flexible tube was evaluated in accordance with the four rankingsA-D given below.

[0124] Rank A:

[0125] No Change in the Appearance; and

[0126] No Occurrence of Cracks and Blisters in Outer Cover.

[0127] Rank B:

[0128] Slight Change in the Appearance; and

[0129] Occurrence of Blisters at a Few Spots of Outer Cover.

[0130] Rank C:

[0131] Large Change in the Appearance; and

[0132] Occurrence of Blisters at Many Spots of Outer Cover.

[0133] Rank D:

[0134] Extremely Large Change in the Appearance; and

[0135] Occurrence of a Large Number of Cracks and Blisters on OuterCover.

[0136] The evaluation results in this test are shown in the attachedTable 1.

[0137] (3-2) Flexibility Test

[0138] A flexibility test was carried out for each of the flexible tubesof Example 1a-1e and Comparative Example 1a-1d. In this test, theflexible tube for an endoscope supported at its both ends was subjectedto bending by 90°, and the flexibility in that state was evaluated inaccordance with the four rankings A-D given below.

[0139] Rank A:

[0140] High Flexibility (A flexible tube of Rank A is considered to bebest suited for use as a flexible tube for an endoscope.)

[0141] Rank B:

[0142] Normal Flexibility (A flexible tube of Rank B is considered to besuited for use as a flexible tube for an endoscope.)

[0143] Rank C:

[0144] Low Flexibility (A flexible tube of Rank C is considered to haveproblems in use as a flexible tube for an endoscope.)

[0145] Rank D:

[0146] Almost No Flexibility (A flexible tube of Rank D is considered tobe unsuited for use as a flexible tube for an endoscope.)

[0147] The result of the flexibility test is shown in the attached Table1.

[0148] (3-3) Durability Test

[0149] A durability test was carried out for each of the flexible tubesof Examples 1a-1e and Comparative Examples 1a-1d. In the durabilitytest, each of the flexible tubes was set to a state where the flexibletube was supported at its both ends, and in this state the operation ofbending by 90° was repeated 300 times. Then, the degree of change in theflexibility after the repeated operation of bending was examined toevaluate the durability of each flexible tube in accordance with thefour rankings A-D given below.

[0150] Rank A:

[0151] Almost No Change in Flexibility (A flexible tube of Rank A isconsidered to have extremely high durability.)

[0152] Rank B:

[0153] Slight Lowering of Flexibility (A flexible tube of Rank B isconsidered to have high durability.)

[0154] Rank C:

[0155] Large Lowering of Flexibility (A flexible tube of Rank C isconsidered to have problems in its durability.)

[0156] Rank D:

[0157] Extremely Large Lowering of Flexibility; and

[0158] Occurrence of cracks and the like at many spots of the outercover.

[0159] (A flexible tube of Rank D is considered to be unsuited for useas a flexible tube for an endoscope.)

[0160] The result of the durability test is shown in the attached Table1.

[0161] (3-4) Evaluation

[0162] The results in the attached Table 1 show that the flexible tubeaccording to the present invention (i.e., Examples 1a -1e) has highchemical resistance and high flexibility as well as high durability.Further, the results in Table 1 also show that conventional flexibletubes (i.e., Comparative Examples 1a-1d) have some drawbacks.

[0163] Specifically, the flexible tube of Comparative Example 1a haspoor resistance to chemical. This drawback is considered to result fromthe fact that the outer layer 32 of the outer cover 3 was made of thematerial with poor chemical resistance. Further, the flexible tube ofComparative Example 1b has poor flexibility. This drawback is consideredto result from the fact that both the inner and outer layers 31 and 32were formed of the materials with relatively high hardness. Furthermore,the flexible tube of Comparative Example 1c has poor flexibility andpoor durability. These drawbacks are considered to result from the factthat no projections 4 as shown in FIG. 2 were formed on the inner layer31. In addition, the flexible tube of Comparative Example 1d has poordurability. This drawback is considered to result from the fact that theinner layer 31 was formed of the material with relatively low hardnessand therefore the projections 4 on the inner layer 31 had poor strength.

[0164] According to the present invention described above, appropriatematerials that are suitable for each of layers of an outer cover 3 areused for preparing an outer cover 3, and the outer cover 3 is providedonto the core body 2 so that each of the layers has appropriatethickness and shape. This structure and the selection of material makeit possible to provide a flexible tube for an endoscope that has highdurability and high flexibility as well as high chemical resistance.

[0165] Further, when a material with high elasticity is used for theintermediate layer of the outer cover, it is possible to give higherflexibility to the flexible tube. In addition, when a material having ahigh adhesion with the core body is used for the inner layer of theouter cover, it is also possible to give high durability to the flexibletube for an endoscope.

III. Second Embodiment (Flexible Tube 1B)

[0166] Next, a second embodiment of the flexible tube for an endoscopewill be described with reference to FIG. 3. FIG. 3 is a sectional viewwhich shows a part of a flexible tube 1B according to the presentinvention, in which illustration of projections 4 as shown in FIG. 2 isomitted, and structure of a reticular tube 22 is simply illustrated as alayer. In this figure, the right-hand side corresponds to the side ofthe base end 11 shown in FIG. 1 (i.e., side closer to an operator), andthe left-hand side corresponds to the side of tip end 12 shown inFIG. 1. In the following, description of the configurations and featuresthat are the same as those in the above-mentioned first embodiment willbe omitted, and description will be given mainly with respect to theconfigurations and features that are different from those of the firstembodiment.

[0167] As shown in FIG. 3, an outer cover (or a portion of the outercover) 3 of the flexible tube 1B has a laminate structure which iscomposed of inner, outer and intermediate layers 31-33. The inner layer31 has a smaller thickness at a portion nearer to the tip end 12 of theflexible tube 1B, while each of the outer and inner layers 32 and 33 hasa substantially uniform thickness over its entire region. This structuregives the outer cover 3 a stiffness (e.g., bending stiffness) thatdecreases in the longitudinal direction from the base end 11 toward thetip end 12. By forming the outer cover 3 such that its stiffness variesin the longitudinal direction, it is possible to give a flexible tubeflexibility that increases in the longitudinal direction from the baseend 11 toward the tip end 12. According to such a flexible tube for anendoscope, since the flexible tube has a higher stiffness in a portioncloser to the base end 11, it is possible to fully transmit to the tipend 12 the push-in force and the rotational force applied by theoperator. On the other hand, since the flexible tube has highflexibility in a portion closer to the tip end 12, it is also possibleto smoothly insert an insertion section (flexible tube) of an endoscopeinto an internal curved portion of a patient in a safe manner.Therefore, the flexible tube 1B as described above makes it possible foran operator to insert the insertion section with easy manipulation, thusenabling the reduction of the burden on the patient during theendoscopic examination.

[0168] In this embodiment, the rate of change in the thickness of theinner layer 31 in the longitudinal direction, that is, the shape of theinner layer 31 is appropriately determined to realize the desired rateof change in the stiffness of the flexible tube in the longitudinaldirection. This makes it possible, for example, to produce various kindsof flexible tubes for an endoscope taking into account various shapes ofinternal portions of a living body, operator's tastes and the like.

[0169] Further, in this embodiment, the value of T1_(min)/T1_(max) isnot particularly limited, where the value of “T1_(min)” is given by thethickness of the thinnest part of the inner layer 31, and the value of“T1_(max)” is given by the thickness of the thickest part of the innerlayer 31. However, the value of T1_(min)/T1_(max) is preferably in therange of 0.05 to 0.95, and more preferably in the range of 0.1 to 0.6.

IV. Third Embodiment (Flexible Tube 1C)

[0170] Next, a third embodiment of the flexible tube for an endoscopewill be described with reference to FIG. 4. FIG. 4 is a sectional viewwhich shows a part of a flexible tube 1C according to the presentinvention, in which illustration of projections 4 as shown in FIG. 2 isomitted, and structure of a reticular tube 22 is simply illustrated as alayer. In this figure, the right-hand side corresponds to the side ofthe base end 11 shown in FIG. 1 (i.e., side closer to an operator), andthe left-hand side corresponds to the side of tip end 12 shown in FIG.1.

[0171] In this embodiment, an outer cover 3 of the flexible tube 1C hasa laminate structure composed of inner, outer and intermediate layers31-33. Each of the inner and intermediate layers 31 and 33 has athickness which gradually varies over its entire region; and the outerlayer 32 has a substantially uniform thickness over its entire region.

[0172] As shown in FIG. 4, the thickness of the inner layer 31 gradually“decreases” in the direction from the base end 11 toward the tip end 12.Conversely, the thickness of the intermediate layer 33 gradually“increases” in the direction from the base end 11 toward the tip end 12.In this embodiment, the intermediate layer 33 is formed of a materialhaving higher elasticity than that of the inner layer 31.

[0173] In this connection, it is to be noted that the thickness of theintermediate layer 33 decreases in the opposite direction to that of theinner layer 31. Further, it is also to be noted that the total thicknessof the inner and intermediate layers 31 and 33 remains substantiallyuniform over the entire region of the outer cover 3, and the thicknessof the outer cover 3 remains substantially uniform over its entireregion, in spite of the fact that the thickness of each of the inner andintermediate layers 31 and 33 varies over its entire region.

[0174] In this embodiment, the value of T3_(min)/T3_(max) is notparticularly limited, where the value of “T3_(min)” is given by thethickness of the thinnest part of the intermediate layer 33, and thevalue of “T3_(max)” is given by the thickness of the thickest part ofthe intermediate layer 33. However, the value of T3_(min)/T3_(max) ispreferably in the range of 0.05 to 0.95, and more preferably in therange of 0.1 to 0.6.

[0175] According to the flexible tube 1C having the structure describedabove, in spite of the fact that the total thickness of the outer cover3 (excluding the portions of the projections 4) is substantially uniformover its entire region, the ratio of the thickness of the intermediatelayer 33 to that of each of the inner and outer layer 31 and 32 becomeslarger at a portion closer to the tip end 12. This structure makes itpossible for the flexible tube 1C to have higher stiffness againsttension and bending at a portion closer to the “base” end 11, and tohave higher flexibility at a portion closer to the “tip” end 12. Inother words, this structure makes it possible for the flexible tube 1Cto have flexibility which gradually varies in the longitudinaldirection.

[0176] According to the flexible tube for an endoscope as describedabove, since the flexible tube has higher stiffness in a portion closerto the base end 11, it is possible to fully transmit to the tip end 12the push-in force and the rotational force applied by the operator. Onthe other hand, the flexible tube has higher flexibility in a portioncloser to the tip end 12, it is also possible to smoothly insert aninsertion section (flexible tube) of an endoscope into an internalcurved portion of a patient in a safe manner. Therefore, the flexibletube as described above makes it possible for an operator to insert theinsertion section with easy manipulation, thus enabling the reduction ofthe burden on the patient during the endoscopic examination.

[0177] Further, according the flexible tube 1C of this embodiment, theouter cover 3 is formed such that the thickness of one of the inner andintermediate layers 31 and 33 decreases in the opposite direction to theother layer. This results in that the flexible tube 1C has a uniformouter diameter over its entire region. When such a flexible tube havinga uniform outer diameter is actually used, it is possible to reduce theburden on the patient during endoscopic examination.

V. Fourth Embodiment (Flexible Tube 1D)

[0178] Next, a fourth embodiment of the flexible tube for an endoscopewill be described with reference to FIG. 5. FIG. 5 is a sectional viewwhich shows a part of a flexible tube 1D according to the presentinvention, in which illustration of projections 4 as shown in FIG. 2 isomitted, and structure of a reticular tube 22 is simply illustrated as alayer. In this figure, the right-hand side corresponds to the side ofthe base end 11 shown in FIG. 1. (i.e., side closer to an operator), andthe left-hand side corresponds, to the side of tip end 12 shown inFIG. 1. Further, in this figure, the reference numeral “I” indicates aregion where a thickness-varying region is formed, and each of thereference numerals “II” and “III” indicates a region where nothickness-varying region is formed. (In this description, a regionwithin which the thickness of a layer increases or decreases is referredto as a “thickness-varying region” of the layer.) In this connection, itis to be noted that the total length of the regions I, II and IIIcorresponds to the length of an outer cover 3 of the flexible tube 1D.

[0179] As shown in FIG. 5, the outer cover 3 of the flexible tube 1D hasa laminate structure composed of inner, outer and intermediate layers31-33. Each of the inner and intermediate layers 31 and 33 has athickness-varying region 34 within the region I, and the outer layer 32has a substantially uniform thickness over its entire region. Thethickness-varying region of each of the inner and intermediate layers 31and 33 has a relatively small length (e.g., approximately 5 to 80 mm).In this embodiment, the intermediate layer 33 is formed of a materialhaving higher elasticity than that of the inner layer 31.

[0180] The thickness-varying region 34 of the inner layer 31 is formedat a specific portion of this layer (i.e., within the region I), and asshown in FIG. 5 the thickness of this thickness-varying region 34gradually decreases within the region I in the direction from the baseend 11 toward the tip end 12. Within the regions II and III the innerlayer 31 has a substantially uniform thickness, but it has largerthickness within the region III as compared with the thickness withinthe region II.

[0181] Similarly the thickness-varying region 34 of the intermediatelayer 33 is also formed within the region I, and as shown in FIG. 5 thethickness of this thickness-varying region 34 gradually decreases withinthe region I in the direction from the tip end 12 toward the base end 11(i.e., in the direction opposite to that of the thickness-varying region34 of the inner layer 31). Within the regions II and III theintermediate layer 32 has a substantially uniform thickness, but it haslarger thickness within the region II as compared with the thicknesswithin the region III.

[0182] It is to be noted that in this embodiment the outer cover 3having the inner, outer and intermediate layers 31-33 is formed so thatthe thickness-varying regions 34 of the inner and intermediate layers 31and 33 face (overlap) each other in the thickness direction as shown inFIG. 5. Further, it is also to be noted that the total thickness of theinner and intermediate layers 31 and 33 remains substantially uniformover the entire region of the flexible tube 1D in spite of the fact thatthese layers have a thickness-varying region.

[0183] According to the flexible tube 1D having the structure describedabove, since the intermediate layer 33 is formed of a material havinghigher elasticity than that of the inner layer 31, the outer cover 3 hasa relatively high stiffness (low flexibility) within the region III,while it has a relatively low stiffness (high flexibility) within theregion II. In addition, the outer cover 3 has a medium stiffness withinthe region I where the thickness-varying regions 34 are formed, and thestiffness of this portion varies in the longitudinal direction. Thestructure described above gives higher stiffness to the base side region(region III) of the flexible tube 1D, while it gives higher flexibilityto the tip side region (region II) of the flexible tube 1D. In addition,the structure described above makes it possible to form a flexible tubesuch that its stiffness (flexibility) varies gradually or stepwisewithin a portion where a thickness-varying region(s) is formed.According to such a flexible tube, since it has higher stiffness in aportion closer to the base end 11, it is possible to fully transmit tothe tip end 12 the push-in force and the rotational force applied by theoperator. On the other hand, the flexible tube has high flexibility in aportion closer to the tip end 12, it is also possible to smoothly insertan insertion section (flexible tube) of an endoscope into an internalcurved portion of a patient in a safe manner. Therefore, the flexibletube as described above makes it possible for an operator to insert theinsertion section with easy manipulation, thus enabling the reduction ofthe burden on the patient during the endoscopic examination.

[0184] Further, according the flexible tube 1D in this embodiment, theflexible tube 1D has a uniform outer diameter over its entire region inspite of the fact that each of the inner and intermediate layers 31 and33 has a thickness-varying region 34. Therefore, when such a flexibletube having a uniform outer diameter is used, it is possible to reducethe burden on the patient during endoscopic examination.

VI. Fifth Embodiment (Flexible Tube 1E)

[0185] Next, a fifth embodiment of the flexible tube for an endoscopewill be described with reference to FIG. 6. FIG. 6 is a sectional viewwhich shows a part of a flexible tube 1E according to the presentinvention, in which illustration of projections 4 as shown in FIG. 2 isomitted, and structure of a reticular tube 22 is simply illustrated as alayer. In this figure, the right-hand side corresponds to the side ofthe base end 11 shown in FIG. 1 (i.e., side closer to an operator), andthe left-hand side corresponds to the side of tip end 12 shown in FIG.1.

[0186] In this embodiment, an outer cover 3 of the flexible tube 1E hasa laminate structure composed of inner, outer and intermediate layers31-33. The inner layer 31 has a substantially uniform thickness over itsentire region. The thickness of each of the outer and intermediatelayers 32 and 33 varies over the entire region. As shown in FIG. 6, thethickness of the outer layer 32 gradually “decreases” in the directionfrom the base end 11 toward the tip end 12. Conversely, the thickness ofthe intermediate layer 33 gradually “increases” in the direction fromthe base end 11 toward the tip end 12. In this embodiment, theintermediate layer 33 is formed of a material having higher elasticitythan that of the outer inner layer 31.

[0187] In this connection, it is to be noted that the thickness of theintermediate layer 33 decreases in the opposite direction to that of theouter layer 32. Further, it is also to be noted that the total thicknessof the outer and intermediate layers 32 and 33 remains substantiallyuniform over the entire region of the flexible tube 1E, and thethickness of the outer cover 3 remains substantially uniform over itsentire region in spite of the fact that the thickness of each of theouter and intermediate layers 32 and 33 varies over its entire region.

[0188] In this embodiment, the value of T2_(min)/T2_(max) is notparticularly limited, where the value of “T2_(min)” is given by thethickness of the thinnest part of the outer layer 32, and the value of“T2_(max)” is given by the thickness of the thickest part of the outerlayer 32. However, the value of T2_(min)/T2_(max) is preferably in therange of 0.05 to 0.95, and more preferably in the range of 0.1 to 0.6.

[0189] According to the flexible tube 1E of this invention, it ispossible to achieve the same advantages as those described with respectto the flexible tube 1C (FIG. 4) in the third embodiment.

VII. Sixth Embodiment (Flexible Tube 1F)

[0190] Next, a sixth embodiment of the flexible tube for an endoscopewill be described with reference to FIG. 7. FIG. 7 is a sectional viewwhich shows a part of a flexible tube 1F according to the presentinvention, in which illustration of projections 4 as shown in FIG. 2 isomitted, and structure of a reticular tube 22 is simply illustrated as alayer. In this figure, the right-hand side corresponds to the side ofthe base end 11 shown in FIG. 1 (i.e., side closer to an operator), andthe left-hand side corresponds to the side of tip end 12 shown inFIG. 1. Further, in this figure, the reference numeral “I” indicates aregion where a thickness-varying region is formed, and each of thereference numerals “II” and “III” indicates a region where nothickness-varying region is formed. In this connection, it is to benoted that the total length of the regions I, II and III corresponds tothe length of an outer cover 3 of the flexible tube 1F.

[0191] As shown in FIG. 7, the outer cover 3 of the flexible tube 1F hasa laminate structure composed of inner, outer and intermediate layers31-33. Each of the outer and intermediate layer 32 and 33 has athickness-varying region 34 within the region I, and the inner layer 31has a substantially uniform thickness over its entire region. Thethickness-varying region 34 of each of the outer and intermediate layers32 and 33 has relatively small length (e.g., approximately 5 to 80 mm).In this embodiment, the intermediate layer 33 is formed of a materialhaving higher elasticity than that of the outer layer 32.

[0192] The thickness-varying region 34 of the outer layer 32 is formedat a specific portion of this layer (i.e., within the region I), and asshown in FIG. 7 the thickness of this thickness-varying region 34gradually decreases within the region I in the direction from the baseend 11 toward the tip end 12. Within the regions II and III the outerlayer 32 has a substantially uniform thickness, but it has largerthickness within the region III as compared with the thickness withinthe region II.

[0193] Similarly the thickness-varying region 34 of the intermediatelayer 33 is also formed within the region I, but as shown in FIG. 7 thethickness of this thickness-varying region 34 gradually decreases withinthe region I in the direction from the tip end 12 toward the tip end 12(i.e., in the direction opposite to that of the thickness-varying region34 of the outer layer 32). Within the regions II and III theintermediate layer 33 has a substantially uniform thickness, but it haslarger thickness within the region II as compared with the thicknesswithin the region III.

[0194] It is to be noted that in this embodiment the outer cover 3having the inner, outer and intermediate layers 31-33 is formed so thatthe thickness-varying regions 34 of the outer and intermediate layers 32and 33 face (overlap) each other in the thickness direction as shown inFIG. 7. Further, it is also to be noted that the total thickness of theouter and intermediate layers 32 and 33 remains substantially uniformover the entire region of the outer cover 3 in spite of the fact thateach of the outer and intermediate layers 32 and 33 has athickness-varying region.

[0195] According to the flexible tube 1F of this invention, it ispossible to achieve the same advantages as those described with respectto the flexible tube 1D in the fourth embodiment.

VIII. Examples of Second-Sixth Embodiments

[0196] Next, specific examples of the second-sixth embodiments describedabove will be described below.

[0197] 1. Preparation of Flexible Tube for an Endoscope

Example 2a

[0198] First, a coil 21 having an outer diameter of 9.9 mm and an innerdiameter of 9.6 mm was prepared by winding a band-shaped stainless steelmaterial having a width of 3 mm. Next, stainless steel fine wires 23 atleast one of which had been given a coating of a polyamide resin andeach of which had a diameter of 0.1 mm were prepared, and then usingthese fine wires a plurality of bundles of ten fine wires were prepared.These bundles of the ten fine wires 23 were woven together in a latticemanner to obtain a reticular tube 22. Then, the obtained reticular tube22 was provided on the prepared coil 21 so that the outer periphery ofthe coil 21 was covered with the reticular tube 22. In this way, a corebody 2 was prepared.

[0199] Next, using an extrusion-molding machine, an outer cover 3composed of inner, outer and intermediate layers 31-33 was provided onthe outer periphery of the core body 2 so that the core body 2 wascovered with the outer cover 3. (A constituent material used for each ofthe layers in this Example is as shown in the attached Table 2.) In thisway, a flexible tube for an endoscope with a length of 1.6 m wasprepared. In this connection, it is to be noted that the length of 1.6 mmeans the length of an available (effective) portion of the flexibletube that can be used for a flexible tube for an endoscope, that is thelength of 1.6 m means an available (effective) length of the flexibletube. Therefore, the actually prepared flexible tube had a length morethan 1.6 m by including additional portions at the both ends of theavailable portion of the flexible tube (See FIG. 13). In this regard,however, it goes without saying that the available length is not limitedto 1.6 m mentioned above.

[0200] In the preparation described above, the outer cover 3 wasprovided over the core body 2 such that the thickness of the inner layer31 gradually increases at a constant rate between both ends 11 and 12 ofthe flexible tube in the direction from the tip end 12 toward base end11. Specifically, the inner layer 31 was formed over the entire region(length) of the outer cover 3 so as to have a thickness of 0.05 mm(T1_(min)) at the tip end 12 and have a thickness of 0.44 mm (T1_(max))at the base end 11. In the inner layer 31 of the prepared flexible tube,the T1_(min)/T1_(max) had a value of 0.125, where the value of“T1_(min)” is given by the thickness of the thinnest part of the innerlayer 31, and the value of “T1_(max)” is given by the thickness of thethickest part of the inner layer 31.

[0201] In addition, the intermediate layer 33 was formed such that itsthickness gradually decreases at a constant rate between the both ends11 and 12 in the direction from the tip end 12 toward base end 11.Specifically, the intermediate layer 33 was formed over the entireregion (length) of the outer cover 3 so as to have a thickness of 0.05mm (T3_(min)) at the base end 11 and have a thickness of 0.4 mm(T3_(max)) at the tip end 12. In the intermediate layer 33 of theprepared flexible tube, the T3_(min)/T3_(max) had a value of 0.125,where the value of “T3_(min)” is given by the thickness of the thinnestpart of the intermediate layer 33, and the value of “T3_(max)” is givenby the thickness of the thickest part of the intermediate layer 33.

[0202] The outer layer 32 of the outer cover 3 was formed over theentire region (length) of the outer cover 3 so as to have a uniformthickness (0.1 mm).

Example 2b

[0203] A flexible tube for an endoscope was prepared in the same manneras in Example 2a except that the thickness (shape) of each layer of anouter cover 3 was changed as follows.

[0204] In the preparation of the flexible tube, the outer cover 3 wasprovided over the core body 2 such that the thickness of the outer layer32 gradually increases at a constant rate between both ends 11 and 12 ofthe flexible tube in the direction from the tip end 12 toward base end11. Specifically, the outer layer 32 was formed over the entire region(length) of the outer cover 3 so as to have a thickness of 0.05 mm(T2_(min)) at the tip end 12 and have a thickness of 0.4 mm (T2_(max))at the base end 11. In the inner layer 31 of the prepared flexible tube,the T2_(min)/T2_(max) had a value of 0.125, where the value of“T2_(min)” is given by the thickness of the thinnest part of the outerlayer 32, and the value of “T2_(max)” is given by the thickness of thethickest part of the outer layer 32.

[0205] In addition, the intermediate layer 33 was formed such that itsthickness gradually decreases at a constant rate between the both ends11 and 12 in the direction from the tip end 12 toward base end 11.Specifically, the intermediate layer 33 was formed over the entireregion (length) of the outer cover 3 so as to have a thickness of 0.05mm (T3_(min)) at the base end 11 and have a thickness of 0.4 mm(T3_(max)) at the tip end 12. In the intermediate layer 33 of theprepared flexible tube, the T3_(min)/T3_(max) had a value of 0.125,where the value of “T3_(min)” is given by the thickness of the thinnestpart of the intermediate layer 33, and the value of “T3_(max)” is givenby the thickness of the thickest part of the intermediate layer 33.

[0206] The inner layer 31 of the outer cover 3 was formed over theentire region (length) of the outer cover 3 so as to have a uniformthickness (0.1 mm).

Example 2c

[0207] A flexible tube for an endoscope was prepared in the same manneras in Example 2a except that the thickness (shape) of each layer of anouter cover 3 was changed as follows.

[0208] In the preparation of the flexible tube, the outer layer 32 ofthe outer cover 3 was formed such that its thickness increases stepwisein four steps in the direction from the tip end 12 to the base end 11.Specifically, the outer layer 32 was formed over the entire region(length) of the outer cover 3 so as to have a thickness of 0.05 mm at afirst quarter (that is closest to the tip end 12) of the entire region;have a thickness of 0.15 mm at a second quarter adjacent to the firstquarter; have a thickness of 0.25 mm at a third quarter adjacent to thesecond quarter; and have a thickness of 0.4 mm at a fourth quarter (thatis closest to the base end 11) adjacent to the third quarter. In thisouter layer 32, the tip end 12 had a thickness of 0.05 mm (T2_(min)),and the base end 11 had a thickness of 0.4 mm (T2_(max)). Thus, theT2_(min)/T2_(max) had a value of 0.125, where the value of “T2_(min)”was given by the thickness of the thinnest part of the outer layer 32,and the value of “T2_(max)” was given by the thickness of the thickestpart of the outer layer 32.

[0209] Further, the intermediate layer 33 of the outer cover 3 wasformed such that the thickness decreases stepwise in four steps in thedirection from the tip end 12 to the base end 11. Specifically, theintermediate layer 33 had been formed over the entire region (length) ofthe outer cover 3 so as to have a thickness of 0.4 mm at a first quarter(that is closest to the tip end 12) of the entire region; have athickness of 0.25 mm at a second quarter adjacent to the first quarter;have a thickness of 0.15 mm at a third quarter adjacent to the secondquarter; and have a thickness of 0.05 mm at a fourth quarter (that isclosest to the base end 11) adjacent to the third quarter. In thisintermediate layer 33, the tip end 12 had a thickness of 0.05 mm(T3_(min)), and the base end 11 had a thickness of 0.44 mm (T3_(max)).Thus, the T3_(min)/T3_(max) had a value of 0.125, where the value of“T3_(min)” was given by the thickness of the thinnest part of theintermediate layer 33, and the value of “T3_(max)” was given by thethickness of the thickest part of the intermediate layer 33.

[0210] In addition, the inner layer 31 of the outer cover 3 was formedover the entire region (length) of the outer cover 3 so as to have auniform thickness (0.1 mm).

Example 2d

[0211] A flexible tube for an endoscope was prepared in the same manneras in Example 2b except that the thickness (shape) of an outer layer 32of an outer cover 3 was changed as follows, and a constituent materialfor the outer layer 32 was changed as shown in the attached Table 2.

[0212] In the preparation of the flexible tube, the outer cover 3 wasprovided over the core body 2 such that the thickness of the outer layer32 gradually increases at a constant rate between the both ends 11 and12 of the flexible tube in the direction from the tip end 12 toward baseend 11. Specifically, the outer layer 32 was formed over the entireregion (length) of the outer cover 3 so as to have a thickness of 0.1 mm(T2_(min)) at the tip end 12 and have a thickness of 0.45 mm (T2_(max))at the base end 11. In the outer layer 32 of the prepared flexible tube,the T2_(min)/T2_(max) had a value of 0.222, where the value of“T2_(min)” was given by the thickness of the thinnest part of the outerlayer 32, and the value of “T2_(max)” was given by the thickness of thethickest part of the outer layer 32.

Example 2e

[0213] A flexible tube for an endoscope was prepared in the same manneras in Example 2a except that a material for an outer layer 32 of anouter cover 3 was changed as shown in the attached Table 2.

Comparative Example 2a

[0214] A core body 2 was prepared in the same manner as in Example 2a.Then, using an extrusion-molding machine, an outer cover 3 composed oftwo layers (i.e., inner and outer layers 31 and 32) was provided on theouter periphery of the core body 2 so that the core body 2 was coveredwith the outer cover 3. In this way, a flexible tube for an endoscopewith a length of 1.6 m was prepared. A constituent material for eachlayer of the outer cover 3 is shown in the attached Table 2.

[0215] In the preparation of the flexible tube in this embodiment, theinner layer 31 of the outer cover 3 was formed over the entire region(length) of the outer cover 3 so as to have a uniform thickness (0.2mm). Further, the outer layer 32 of the outer cover 3 was formed overthe entire region (length) of the outer cover 3 so as to have a uniformthickness (0.3 mm).

Comparative Example 2b

[0216] A flexible tube for an endoscope was prepared in the same manneras in Comparative Example 2a except that a material for an outer layer32 was changed as shown in the attached Table 2.

Comparative Example 2c

[0217] A flexible tube for an endoscope was prepared in the same manneras in Comparative Example 2a except that a material for each of innerand outer layers 31 and 32 was changed as shown in the attached Table 2.

[0218] 2. Observation of the Prepared Flexible Tubes

[0219] An observation of the cross-section of the outer cover 3 wascarried out for each of the flexible tubes of Examples 2a-2e andComparative Examples 2a-2c. Through the observation, formation ofprojections 4 as shown in FIG. 2 was observed in each of the flexibletubes of Examples 2a-2e and Comparative Examples 2a and 2b, but noformation of projections 4 was observed in the flexible tube ofComparative Example 2c.

[0220] 3. Measurement of Rate of Change in Bending Stiffness

[0221] The rate of change in the bending stiffness in the longitudinaldirection was measured for each of the flexible tubes of Examples 2a-2e.

[0222] For each flexible tube, first the flexible tube was divided intoeight sections (i.e., first-eighth sections as shown in FIG. 13) whichhave an equal length (200 mm) in the longitudinal direction, and thenthe bending stiffness in “each” of the eight sections of the flexibletube was measured according to the following method.

[0223] In the measurement, as shown in FIG. 15, first the flexible tubewas laid on two supporting-points located a distance L (200 mm) a partso that both ends of one of the sections were supported by the twosupporting-points. Then, the magnitude of the pressing force F when thecentral point of the section was displaced downward by a predetermineddistance y (50 mm) was measured and defined as the bending stiffness ofeach section. Based on the measured value, the rate of change in thebending stiffness in the longitudinal direction of the flexible tube wascalculated. The results of the measurement are shown in the attachedTable 3.

[0224] 4. Evaluation of Flexible Tube

[0225] (4-1) Insertion (Operationability) Test

[0226] An insertion test was carried out for each of the flexible tubesof Examples 2a-2e and Comparative Examples 2a-2c to evaluateoperationability (i.e., degree of easiness in insertion operation) of anendoscope with the flexible tube.

[0227] Before carrying out the insertion test, endoscopes as shown inFIG. 1 were prepared using the flexible tubes of Examples 2a-2e andComparative Examples 2a-2c. Further, a living body model having aninternal structure similar to an internal portion of a human body wasprepared. Then, each of the prepared endoscopes was inserted into theinternal portion of the living body model until its tip end (i.e., tipof an bendable tube 5) reaches a portion corresponding to a largeintestine of a human body. In the insertion test, the operationabilityof the endoscope during the insertion operation was evaluated inaccordance with the four rankings A-D given below.

[0228] Rank A:

[0229] It is possible to perform insertion operation very smoothly. (Aflexible tube of an endoscope of Rank A is considered to be best suitedfor use as a flexible tube for an endoscope.)

[0230] Rank B:

[0231] It is possible to perform insertion operation smoothly. (Aflexible tube of an endoscope of Rank B is considered to be suited foruse as a flexible tube for an endoscope.)

[0232] Rank C:

[0233] It takes a relatively long time to complete insertion operation.(A flexible tube of an endoscope of Rank C is considered to haveproblems for use as a flexible tube for an endoscope.)

[0234] Rank D:

[0235] It is difficult to complete insertion operation. (A flexible tubeof an endoscope of Rank D is considered to be unsuited for use as aflexible tube for an endoscope.)

[0236] The results of the insertion test are shown in the attached Table4.

[0237] (4-2) Chemical Resistance Test

[0238] A chemical resistance test was carried out for each of theflexible tubes of Example 2a-2e and Comparative Example 2a-2c. In thechemical resistance test, 100L of 10% aqueous solution of iodine held at25° C. was prepared first, and then each of the prepared flexible tubeswas immersed in the aqueous solution for 200 hours. Then, the conditionof each flexible tube was evaluated in accordance with the four rankingsA-D given below.

[0239] Rank A:

[0240] No Change in the Appearance; and

[0241] No Occurrence of Cracks and Blisters in Outer Cover.

[0242] Rank B:

[0243] Slight Change in the Appearance; and

[0244] Occurrence of Blisters at a Few Spots of Outer Cover.

[0245] Rank C:

[0246] Large Change in the Appearance; and

[0247] Occurrence of Blisters at Many Spots of Outer Cover.

[0248] Rank D:

[0249] Extremely Large Change in the Appearance; and

[0250] Occurrence of a Large Number of Cracks and Blisters on OuterCover.

[0251] The evaluation result in this test is shown in the attached Table4.

[0252] (4-3) Durability Test

[0253] A durability test was carried out to examine durability of eachof the flexible tubes of Example 2a-2e and Comparative Example 2a-2c. Inthe durability test, each of the flexible tubes was set to a state wherethe flexible tube was supported at its both ends, and in this state theoperation of bending by 90° was repeated 300 times for each flexibletube. Then, the degree of change in the flexibility after the repeatedoperation of bending was examined to evaluate the durability of theflexible tube in accordance with the four rankings A-D given below.

[0254] Rank A:

[0255] Almost No Change in Flexibility (A flexible tube of Rank A isconsidered to have extremely high durability.)

[0256] Rank B:

[0257] Slight Lowering of Flexibility (A flexible tube of Rank B isconsidered to have high durability.)

[0258] Rank C:

[0259] Large Lowering of Flexibility (A flexible tube of Rank C isconsidered to have problems in the durability.)

[0260] Rank D:

[0261] Extremely Large Lowering of Flexibility; and

[0262] Occurrence of cracks and the like at many spots of the outercover.

[0263] (A flexible tube of Rank D is considered to be unsuited for useas a flexible tube for an endoscope.)

[0264] The result of the durability test is shown in the attached Table4.

[0265] (4-4) Evaluation

[0266] The results in the attached Tables 3 and 4 show that the flexibletube according to the present invention (i.e., Examples 2a-2e) hasexcellent operationability and high chemical resistance as well as highdurability. Further, the results in the attached Table 4 also show thatconventional flexible tubes (i.e., Comparative Examples 2a-2c) have somedrawbacks.

[0267] Specifically, the flexible tube of Comparative Example 2a haspoor resistance to chemical. This drawback is considered to result fromthe fact that the outer layer 32 of the outer cover 3 was formed of thematerial having poor chemical resistance. Further, the flexible tube ofComparative Example 2b has poor operationability. Furthermore, theflexible tube of Comparative Example 2c has poor durability as well aspoor operationability. The poor durability of this flexible tube isconsidered to result from the fact that no projections 4 as shown inFIG. 2 were formed on the inner layer 31.

[0268] According to the present invention described above, appropriatematerials that are for each of layers of an outer cover 3 are used forpreparing the outer cover, and the outer cover 3 is provided onto thecore body so that each of the layers has appropriate thickness andshape. This structure and the selection of material make it possible toproduce a flexible tube for an endoscope that has high durability, highflexibility, and high chemical resistance as well as excellentoperationability.

[0269] Further, according to the present invention, the outer cover ofthe flexible tube is formed so that the thickness of at least one oflayers constituting the outer cover (laminate structure) varies in thelongitudinal direction, for example, gradually or stepwise. Thisconfiguration makes it possible for an operator to insert an insertionsection (flexible tube) of an endoscope into a body cavity of a livingbody with easy manipulation.

[0270] Furthermore, according to the present invention, a materialhaving high elasticity is used for an intermediate layer of the outercover. This makes it possible to give high flexibility to a flexibletube, thus enabling the operator to insert an insertion section of anendoscope more easily.

[0271] Moreover, according to the present invention, a material havinghigh resistance to chemical is used for an outer layer of the outercover. This makes it possible to give high chemical resistance to aflexible tube.

[0272] In addition, according to the present invention, a materialhaving high adhesion with a core body 2 is used for an inner layer of anouter cover. This makes it possible to give high durability to aflexible tube.

IX. Seventh Embodiment (Flexible Tube 1G)

[0273] Next, a seventh embodiment of the flexible tube for an endoscopewill be described with reference to FIG. 8. FIG. 8 is a sectional viewwhich shows a part of a flexible tube 1G according to the presentinvention, in which illustration of projections 4 as shown in FIG. 2 isomitted, and structure of a reticular tube 22 is simply illustrated as alayer. In this figure, the right-hand side corresponds to the side ofthe base end 11 shown in FIG. 1 (i.e., side closer to an operator), andthe left-hand side corresponds to the side of tip end 12 shown in FIG.1.

[0274] An outer cover 3 of the flexible tube 1G has a laminate structurecomposed of inner, outer and intermediate layers 31-33. The inner andouter layers 31 and 32 have the same structures as those of the flexibletube 1A in the first embodiment, and this embodiment is different fromthe first embodiment in the structure of the intermediate layer 33. Thestructure of the intermediate layer 33 is described below in detail.

[0275] The intermediate layer 33 is formed between the inner layer 31and the outer layer 32. As shown in FIG. 8, this intermediate layer 33has a first portion (first region) 31 a formed at a position closer tothe tip end 12, and a second portion (second region) 33 b formed at aposition closer to the base end 11. The first and second portions 33 aand 33 b are contiguous to each other through a boundary 34.Specifically, the first portion 33 a is formed within a region from thetip end 12 to the boundary 34, and the second portion 33 b is formedwithin a region from the boundary section 34 to the base end 11.

[0276] The first portion 33 a is different from the second portion 33 band 33 b in its physical property or chemical property. (Hereinafter,the physical property and chemical property will be referred to simplyas “property.”) However, the property within each of the first andsecond portions 33 a and 33 b is substantially homogeneous. As a resultof this structure, the property of the intermediate layer 33 variessubstantially stepwise at the boundary 34. Such a difference in theproperty between the first and second portions 33 a and 33 b can beobtained by constituting the first and second portions 33 a and 33 bwith different materials.

[0277] The lengths of the first and second portions 33 a and 33 b in thelongitudinal direction may differ depending on the type of an endoscopeor the like. However, in this invention, it is preferable that thelength of the first portion 33 a is in the range of about 50 to 1000 mm,and more preferably about 100 to 700 mm. Further, it is preferable thatthe length of the second portion 33 b is in the range of about 50 to1000 mm, and more preferably 100 to 700 mm.

[0278] In addition, in this invention, it is preferable that the firstportion 33 a is formed of a material having a lower hardness (stiffness)than that of the second portion 33 b. With this arrangement, the tipside portion of the outer cover 3 where the first portion 33 a is formedhas a lower stiffness against tension, bending and the like than that ofthe base side portion of the outer cover 3 where the second portion 33 bis formed. Therefore, by forming the outer cover 3 so as to have twodistinct portions (i.e., first and second portion 33 a and 33 b), itbecomes possible to give the tip side region of a flexible tube a higherflexibility than that of the base side region.

[0279] According to the flexible tube 1G having the intermediate layer33 as described, the flexible tube 1G has a high “stiffness” in theportion near the base end 11 (where the second portion 33 b is formed)so that a push-in force and the rotational force applied by the operatorare sufficiently transmitted to the tip end 12, while it has a high“flexibility” in the portion near the tip end 12 (where the firstportion 33 a is formed) so that the tip side region of the flexible tubeis smoothly inserted into and follows the body cavity having curvedform. This structure makes it possible to improve the operationabilityof the endoscope when inserting the insertion section (flexible tube)into an internal portion of the living body. Accordingly, when anendoscope with the flexible tube having the structure as described aboveis used during an endoscopic examination, it is possible to reduceburden on a patient, since the operator can safely and smoothly performthe insertion operation.

[0280] In this invention, it is preferable the intermediate layer 33 hasa higher elasticity than that of the outer layer 32, and more preferablythe intermediate layer 33 has a higher elasticity than that of any oneof the inner and outer layers 31 and 32. With this arrangement, theintermediate layer 33 functions as a cushioning layer (cushioning means)between the inner layer 31 and the outer layer 32. (In the following,such a function given by the intermediate layer 33 is referred to as“cushioning function.”) Accordingly, by forming the, intermediate layer33 as described above, it is possible to give higher flexibility to theflexible tube.

[0281] Hereinafter, the cushioning function of the intermediate layer 33is described in more detail. When the flexible tube 1G is bent by anexternal force, the high elastic force is generated in the bentintermediate layer 33 through the deformation thereof The generatedelastic force is transmitted effectively to the inner layer 31 and theouter layer 32, respectively, since the intermediate layer 33 issandwiched between the inner layer 31 and the outer layer 32 each ofwhich has relatively low elasticity. When the external force has beenremoved, the bent flexible tube 1G is restored to its original shape bythe high elastic force generated in the bent intermediate layer 33. Inthis connection, it is to be noted that the restoration of the flexibletube into its original shape is achieved by the cushioning function ofthe intermediate layer 33, and that such a cushioning function gives theflexible tube high flexibility.

[0282] In this embodiment, a constituent material for the intermediatelayer 33 is not particularly limited. Examples of such material includevarious resins having elasticity such as polyvinyl chloride, polyolefine(e.g., polyethylene, polypropylene, ethylene-vinylacetate copolymer andthe like), polyamide, polyester (e.g., polyethylene terephthalate (PET),polybutylene terephthalate and the like), polyurethane, polystyreneresin, fluoro-based resin (e.g., polytetrafluoroethylene,ethylene-tetrafluoroethylene copolymer and the like), polyimide, and thelike; and various elastomers such as polyurethane-based elastomer,polyester-based elastomer, polyolefine-based elastomer, polyamide-basedelastomer, polystyrene-based elastomer, fluorine-based elastomer,silicone rubber, fluororubber, latex rubber, and the like. These can beused alone or as a mixture of two or more thereof. In this invention, amaterial containing at least one of low hardness polyurethane-basedelastomer, low hardness polyolefin-based elastomer, and low hardnesspolyester-based elastomer is preferably used to form the intermediatelayer 33, since such elastomers have high elasticity.

[0283] Although the intermediate layer 33 in this embodiment is given asingle layer construction, it may be given a construction of two or morelayers.

[0284] In this invention, the average thickness of the intermediatelayer 33 is not particularly limited, but the average thickness ispreferably in the range of 0.05 to 0.8 mm, and more preferably in therange of 0.05 to 0.4 mm.

X. Eighth Embodiment (Flexible Tube 1H)

[0285] Next, an eighth embodiment of the flexible tube for an endoscopewill be described with reference to FIG. 9. FIG. 9 is a sectional viewwhich shows a part of a flexible tube 1H according to the presentinvention, in which illustration of projections 4 as shown in FIG. 2 isomitted, and structure of a reticular tube 22 is simply illustrated as alayer. In this figure, the right-hand side corresponds to the side ofthe base end 11 shown in FIG. 1 (i.e., side closer to an operator), andthe left-hand side corresponds to the side of tip end 12 shown in FIG.1.

[0286] As shown in FIG. 9, the outer cover 3 of the flexible tube 1H hasa laminate structure composed of inner, outer and intermediate layers31-33. Each of the inner and outer layers 31 and 32 has a substantiallyuniform thickness over its entire region, and has almost homogeneousproperty over its entire region. The intermediate layer 33 has a firstportion (first region) 33 a formed in a tip side region, and a secondportion (second region) 33 b formed in a base side region. The first andsecond portions 33 a and 33 b of the intermediate layer 33 havedifferent properties. As shown in FIG. 9, the first and second portions33 a and 33 b are contiguous to each other through a boundary part(property-varying region) 37 formed between the first and secondportions 33 a and 33 b, and they are arranged along the longitudinaldirection. In this invention, it is preferable that the first portion 33a is formed of a material having a lower hardness (stiffness) than thatof a material constituting the second portion 33 b.

[0287] Within the boundary part 37, its property gradually varies in thelongitudinal direction. A tip end portion of the boundary part 37 hassubstantially the same property as that of the first portion 33 a, whilea base end portion of the boundary part 37 has substantially the sameproperty as that of the second portion 33 b.

[0288] The boundary part 37 described above is formed through anextrusion molding process. Specifically, a mixture of a constituentmaterial for the first portion 33 a and a constituent material for thesecond portion 33 b is prepared first, and then the mixture is fedduring the extrusion molding while gradually changing the mixing rate ofthese materials. In this way, the outer cover 3 which has a layer with aboundary part where its property changes gradually in the longitudinaldirection is formed. However, the structure of the boundary part 37 isnot limited to that as described above. For example, the boundary part37 may be formed as a laminated part (composite part) composed of twohalves. In this case, a first half is formed of a material having thesame property as the first portion 33 a such that its thicknessgradually decreases in the direction from the tip side to the base side.Further, a second half is formed of a material having the same propertyas the second portion 33 b such that its thickness gradually decreasesin the direction from the base side to the tip side.

[0289] The length in the longitudinal direction of the boundary part 37is not particularly limited. For example, when the boundary part 37 isformed so as to have a relatively large length, it is possible give aflexible tube a stiffness which varies more gradually in thelongitudinal direction. However, in this invention, the length of theboundary part 37 is preferably in the range of 5 to 600 mm, and morepreferable in the range of 10 to 400 mm.

[0290] By configuring a flexible tube as described above, it is possibleto form an intermediate layer so as to have relatively low stiffness inthe first portion 33 a located at the tip side, and have relatively highstiffness in the second portion 33 b located at the base side. Inaddition, it is also possible to form the intermediate layer 33 suchthat a boundary part (property-varying region) 37 where its propertyvaries gradually along the longitudinal direction is formed between thefirst and second portions 33 a and 33 b.

[0291] According to the flexible tube as described above, due to theformation of the boundary part 37 as well as the homogeneous formationof the inner and outer layers 31 and 32, the stiffness of the flexibletube 1H gradually varies within the boundary part 37 and in the vicinityof its both ends. This structure makes it possible to provide a flexibletube whose stiffness (e.g., bending stiffness) varies more graduallyalong the longitudinal direction as compared with the flexible tube 1G(FIG. 8) of the seventh embodiment described above. When an endoscopewith the flexible tube having the structure as described above is usedduring an endoscopic examination, it is possible to reduce burden on apatient, since the operator can more safely and smoothly insert theinsertion portion of the endoscope into a body cavity of the patient.

[0292] Further, according to the flexible tube 1H of this embodiment,there is no spot where the stiffness varies abruptly, since theintermediate layer 33 has the boundary part (property-varying region)37, and the inner and outer layers 31 and 32 are formed almosthomogeneously. Therefore, a push-in force or a rotational force appliedby the operator from the base side will not be concentrated at anyportion, so that the force can be transmitted sufficiently to the tipend of an endoscope with the flexible tube. In addition, because of theabsence of a spot where the stiffness varies abruptly, tendency of theflexible tube to curl or twist will not concentrate at any portion ofthe flexible tube.

[0293] In addition, according to the flexible tube of this embodiment,each of the inner and outer layers 31 and 32 is formed homogeneouslyover its entire region. This formation makes it possible for the innerlayer 31 to have a uniform and high adhesion with the core body 2 overits entire region, and also makes it possible for the outer layer 32 tohave uniform and high resistance to chemical over its entire length.

XI. Ninth Embodiment (Flexible Tube 1I)

[0294] Next, a ninth embodiment of the flexible tube for an endoscopewill be described with reference to FIG. 10. FIG. 10 is a sectional viewwhich shows a part of a flexible tube 1I according to the presentinvention, in which illustration of projections 4 as shown in FIG. 2 isomitted, and structure of a reticular tube 22 is simply illustrated as alayer. In this figure, the right-hand side corresponds to the side ofthe base end 11 shown in FIG. 1 (i.e., side closer to an operator), andthe left-hand side corresponds to the side of tip end 12 shown in FIG.1.

[0295] As shown in FIG. 10, an outer cover 3 of the flexible tube 1I hasa laminate structure composed of inner, outer and intermediate layers31-33. Each of the inner and outer layers 31 and 32 has a substantiallyuniform thickness and a substantially homogeneous property over itsentire region. The intermediate layer 33 has three distinct portions(i.e., first-third portions 33 a-33 c). The first portion (first region)33 a is formed at the tip side, the third portion (third region) 33 c isformed at the base side, and the second portion (second region) 33 b isformed between the first portion 33 a and the third portion 33 c. Eachof the first and third portions 33 a and 33 c is different from thesecond portion 33 b in its property. In this invention, it is preferablethat the first portion 33 a is formed of a material having a lowerhardness (stiffness) than that of a material constituting the secondportion 33 b. Further, it is also preferable that the second portion 33b is formed of a material having a lower hardness (stiffness) than thatof a material constituting the third portion 33 c.

[0296] In addition, the intermediate layer 33 has two boundary parts(property-varying regions) 37 which are formed between the first andsecond portions 33 a and 33 b and between the second and third portions33 b and 33 c, respectively. Each of the boundary parts 37 hassubstantially the same structure as that of the intermediate layer 33 ofthe flexible tube 1H (FIG. 9) in the eighth embodiment described above,and formed in the same manner as in the eighth embodiment.

[0297] In this embodiment, the length of each of the portions of theintermediate layer 33 is not particularly limited. However, it ispreferable that the length of the first portion 33 a is preferably inthe range of about 50 to 1000 mm, and more preferably in the range ofabout 100 to 700 mm. Further, it is preferable that the length of thesecond portion 33 b is preferably in the range of about 50 to 800 mm,and more preferably in the range of about 100 to 600 mm. Furthermore, itis preferable that the length of the third portion 33 c is preferably inthe range of about 50 to 1000 mm, and more preferably in the range ofabout 200 to 1000 mm.

[0298] According to the flexible tube 1I having the structure describedabove, the intermediate layer 33 has a relatively low stiffness in thefirst portion 33 a located at the tip side, has a relatively highstiffness in the third portion 33 c located at the base side, and has amedium stiffness in the second portion 33 b between the first and secondportions 33 a and 33 b. In addition, the stiffness of the intermediatelayer 33 gradually varies within each of the boundary parts 37 formedbetween the first and second portions 33 a and 33 b and between thesecond and third portions 33 b and 33 c, respectively.

[0299] Further, according to the flexible tube 1I described above, as aresult of the formation of the three distinct portions 33 a-33 c, thestiffness of the flexible tube 1I varies along the longitudinaldirection in roughly three stages. In addition, as a result of theformation of the two boundary parts (property-varying regions) 37, thestiffness of the flexible tube 1I varies more gradually along thelongitudinal direction. Accordingly, the stiffness of the flexible tube1I in this embodiment varies along the longitudinal direction in a moregradual manner as compared with the flexible tube 1H (FIG. 9) of theeighth embodiment in which the stiffness varies in roughly “two” stages.Therefore, when an endoscope with the flexible tube 1I having thestructure as described above is used during an endoscopic examination,it is possible to reliably reduce burden on a patient, since theoperator can more safely and smoothly insert an insertion portion of anendoscope.

XII. Tenth Embodiment (Flexible Tube 1J)

[0300] Next, a tenth embodiment of the flexible tube for an endoscopewill be described with reference to FIG. 11. FIG. 11 is a sectional viewwhich shows a part of a flexible tube 1J according to the presentinvention, in which illustration of projections 4 as shown in FIG. 2 isomitted, and structure of a reticular tube 22 is simply illustrated as alayer. In this figure, the right-hand side corresponds to the side ofthe base end 11 shown in FIG. 1 (i.e., side closer to an operator), andthe left-hand side corresponds to the side of tip end 12 shown in FIG.1.

[0301] As shown in FIG. 11, an outer cover 3 of the flexible tube 1J hasa laminate structure composed of inner, outer and intermediate layers31-33. Each of the inner and intermediate layers 31 and 33 hashomogeneous formation and a substantially uniform thickness over itsentire region. The outer layer 32 has three distinct portions (i.e.,first-third portions 32 a-32 c). The first portion (first region) 32 ais formed at the tip side, the third portion (third region) 32 c isformed at the base side, and the second portion (second region) 32 b isformed between the first portion 32 a and the third portion 32 c. Eachof the first and third portions 32 a and 32 c is different from thesecond portion 32 b in its property. In this invention, it is preferablethat the first portion 32 a is formed of a material having a lowerhardness (stiffness) than that of a material constituting the secondportion 32 b. Further, it is also preferable that the second portion 32b is formed of a material having a lower hardness (stiffness) than thatof a material constituting the third portion 32 c. In addition, in thisinvention, it is preferable that each of the first-third portions 32a-32 c of the outer layer 32 has high resistance to chemical.

[0302] The outer layer 32 has two boundary parts (property-varyingregions) 36 which are formed between the first and second portions 32 aand 32 b and between the second and third portions 32 b and 32 c,respectively. Each of the boundary parts 36 has substantially the samestructure as that of the intermediate layer 33 of the flexible tube 1H(FIG. 9) in the eighth embodiment described above, and formed in thesame manner as in the eighth embodiment.

[0303] In this embodiment, the length of each of the portions of theouter layer 32 is not particularly limited. However, it is preferablethat the length of the first portion 32 a is preferably in the range ofabout 50 to 1000 mm, and more preferably in the range of about 100 to700 mm. Further, it is preferable that the length of the second portion32 b is preferably in the range of about 50 to 800 mm, and morepreferably in the range of about 100 to 600 mm. Furthermore, it ispreferable that the length of the third portion 32 c is preferably inthe range of about 50 to 1000 mm, and more preferably in the range ofabout 200 to 1000 mm.

[0304] In the flexible tube 1J having the structure described above, theouter layer 32 has a relatively low stiffness in the first portion 32 alocated at the tip side, has a relatively high stiffness in the thirdportion 32 c located at the base side, and has a medium stiffness in thesecond portion 32 b between the first and third portions 32 a and 32 c.In addition, the stiffness of the outer layer 32 gradually varies withineach of the boundary parts (property-varying regions) 36 formed betweenthe first and second portions 32 a and 32 b and between the second andthird portions 32 b and 32 c, respectively. Therefore, according to theflexible tube 1J described above, it is possible to achieve the sameadvantages as those described with respect to the flexible tube 1I (FIG.10) in the ninth embodiment.

[0305] In addition, according to the flexible tube 1J of thisembodiment, each of the inner and intermediate layers 31 and 33 isformed homogeneously over its entire region. This formation makes itpossible for the inner layer 31 to have a uniform and high adhesion withthe core body 2 over its entire region, and also makes it possible forthe intermediate layer 33 to have uniform and high flexibility over itsentire length.

XIII. Eleventh Embodiment (Flexible Tube 1K)

[0306] Next, an eleventh embodiment of the flexible tube for anendoscope will be described with reference to FIG. 12. FIG. 12 is asectional view which shows a part of a flexible tube 1K according to thepresent invention, in which illustration of projections 4 as shown inFIG. 2 is omitted, and structure of a reticular tube 22 is simplyillustrated as a layer. In this figure, the right-hand side correspondsto the side of the base end 11 shown in FIG. 1 (i.e., side closer to anoperator), and the left-hand side corresponds to the side of tip end 12shown in FIG. 1.

[0307] As shown in FIG. 12, an outer cover 3 of the flexible tube 1K hasa laminate structure composed of inner, outer and intermediate layers31-33.

[0308] The intermediate layer 33 has a substantially uniform thicknessover its entire region, and is formed homogeneously over its entireregion.

[0309] The outer layer 32 has the same structure as that described withreference to the tenth embodiment shown in FIG. 11. Specifically, theouter layer 32 has three distinct portions (i.e., first-third portions32 a-32 c). The first portion (first region) 32 a is formed at the tipside, the third portion (third region) 32 c is formed at the base side,and the second portion (second region) 32 b is formed between the firstportion 32 a and the third portion 32 c. Each of the first and thirdportions 32 a and 32 c is different from the second portion 32 b in itsproperty. In this invention, it is preferable that the first portion 32a is formed of a material having a lower hardness (stiffness) than thatof a material constituting the second portion 32 b. Further, it is alsopreferable that the second portion 32 b is formed of a material having alower hardness (stiffness) than that of a material constituting thethird portion 32 c. In addition, in this invention, it is preferablethat each of the first-third portions 32 a-32 c of the outer layer 32has high resistance to chemical.

[0310] Further, the outer layer 32 has two boundary parts(property-varying regions) 36 which are formed between the first andsecond portions 32 a and 32 b and between the second and third portions32 b and 32 c, respectively. Each of the boundary parts 36 hassubstantially the same structure as that of the intermediate layer 33 ofthe flexible tube 1H (FIG. 9) in the eighth embodiment described above,and formed in the same manner ass in the eighth embodiment.

[0311] The inner layer 31 has two distinct portions (i.e., first andsecond portions 31 a and 31 b). The first portion (first region) 31 a isformed at the tip side, and the second portion (second region) 31 b isformed at the base side. The first portion 31 a is different from thesecond portion 31 b in its property. In this invention, it is preferablethat the first portion 31 a is formed of a material having a lowerhardness (stiffness) than that of a material constituting the secondportion 31 b. Further, it is also preferable that each of the first andsecond portions 31 a and 31 b of the inner layer 31 is formed of amaterial having high adhesion with a core body 2, that is, a materialwhich are easily formed into a layer with projections 4 as shown in FIG.2 through extrusion molding.

[0312] In addition, the inner layer 31 has a boundary part(property-varying region) 35 which is formed between the first andsecond portions 31 a and 31 b. The boundary part 35 has substantiallythe same structure as that of the intermediate layer 33 of the flexibletube 1H (FIG. 9) in the eighth embodiment described above, and formed inthe same manner as in the eighth embodiment.

[0313] In this embodiment, the length of the first and second portions31 a and 31 b of the inner layer 31 is not particularly limited.However, it is preferable that the length of the first portion 31 a ispreferably in the range of about 50 to 1000 mm, and more preferably inthe range of about 500 to 1000 mm. Further, it is preferable that thelength of the second portion 31 b is preferably in the range of about 50to 1000 mm, and more preferably in the range of about 400 to 1000 mm.

[0314] According to the flexible tube 1K having the structure describedabove, the outer cover 3 of the flexible tube 1K has different stiffnessin the following four regions (1)-(4). (The stiffness of the flexibletube 1K increases in this order in the longitudinal direction.)

[0315] (1) A region of the outer cover 3 where both the first portion 32a of the outer layer 32 and the first portion 31 a of the inner layer 31are formed, and where these portions partly face each other.

[0316] (2) A region of the outer cover 3 where both the second portion32 b of the outer layer 32 and the first portion 31 a of the inner layer31 are formed, and where these portions partly face each other.

[0317] (3) A region of the outer cover 3 where both the second portion32 b of the outer layer 32 and the second portion 31 b of the innerlayer 31 are formed, and where these portions partly face each other.

[0318] (4) A region of the outer cover 3 where both the third portion 32c of the outer layer 32 and the second portion 31 b of the inner layer31 are formed, and where these portions partly face each other.

[0319] Therefore, the flexibility of the flexible tube 1K varies alongthe longitudinal-direction in roughly four stages. Further, as a resultof the formation of the boundary parts (property-varying regions) 35 and36, the stiffness of the flexible tube varies more gradually along thelongitudinal direction. Accordingly, the stiffness of the flexible tube1K in this embodiment varies along the longitudinal direction in a moregradual manner as compared with the flexible tube 1I (FIG. 10) of theninth embodiment in which the stiffness varies in roughly “three”stages. Therefore, when an endoscope with the flexible tube having thestructure as described above is used during an endoscopic examination,it is possible to reliably reduce burden on a patient, since theoperator can more safely and smoothly insert the insertion portion ofthe endoscope into a body cavity of the patient.

[0320] Further, according to the flexible tube 1K having the structuredescribed above, the outer cover 3 of the flexible tube 1K is formedsuch that the boundary part 35 of the inner layer 31 is not locatedbelow the boundary parts 36 of the outer layer 32 in the thicknessdirection. In other words, the outer cover 3 of the flexible tube isformed such that the boundary part 35 of the inner layer 31 and theboundary part 36 of the outer layer 32 are alternately located in thelongitudinal direction of the outer cover 3. This arrangement makes itpossible for a flexible tube to have a stiffness that varies moregradually in the longitudinal direction.

XIV. Examples of Modification

[0321] In the above, the flexible tube for an endoscope according to thepresent invention was described in detail. However, it is to be notedthat this invention is not limited to the embodiments described above.

[0322] For example, one or more of layers of the outer cover 3 may beformed using materials which contain the same principal material (mainpolymer) but which are different in molecular weight, the content ofadditives (e.g., plasticizer), or the like. Alternatively, one or moreof layers of the outer cover 3 may also be formed of materials whichcontain the same components but which are different in density. In thisway, it is also possible to form an outer cover 3 such that a layer ofthe outer cover 3 has distinct portions having different properties.

[0323] Further, the structure of each layer of the outer cover 3 is notparticularly limited. For example, an outer cover 32 of a flexible tubemay be formed such that any one of layers has regions having differentproperties. Further, an outer cover of a flexible tube may also beformed such that each of two or more of layers has regions havingdifferent properties.

[0324] Furthermore, the structure of an outer cover 3 described above isnot particularly limited. For example, an outer cover of a flexible tubemay be formed such that a part of the outer cover has a laminatestructure composed of a plurality of layers.

[0325] In addition, for example, the flexible tube for an endoscopeaccording to the present invention may be applied to other site of theendoscope such as a flexible tube for a light guide connected to a lightsource device.

XV. Examples of Seventh-Eleventh Embodiments

[0326] Next, specific examples of the seventh-eleventh embodiments ofthe present invention will be described below.

[0327] 1. Preparation of Flexible Tube for an Endoscope

Example 3a

[0328] First, a coil 21 having an outer diameter of 9.9 mm and an innerdiameter of 9.6 mm was prepared by winding a band-shaped stainless steelmaterial having a width of 3 mm. Next, stainless steel fine wires 23 atleast one of which had been given a coating of a polyamide resin andeach of which had a diameter of 0.1 mm were prepared, and then usingthese fine wires a plurality of bundles of ten fine wires were prepared.These bundles of the ten fine wires 23 were woven together in a latticemanner to obtain a reticular tube 22. Then, the obtained reticular tube22 was provided on the prepared coil 21 so that the outer periphery ofthe coil 21 was covered with the reticular tube 22. In this way, a corebody 2 was prepared.

[0329] Next, using an extrusion-molding machine, an outer cover 3composed of inner, outer and intermediate layers 31-33 was provided onthe outer periphery of the core body 2 so that the core body 2 wascovered with the outer cover 3. In this way, a flexible tube for anendoscope with a length of 1.6 m was prepared. In this connection, it isto be noted that the length of 1.6 m means the length of an available(effective) portion of the flexible tube that can be used for a flexibletube for an endoscope, that is the length of 1.6 m means an available(effective) length of the flexible tube. Therefore, the actuallyprepared flexible tube had a length more than 1.6 m by includingadditional portions at the both ends of the available portion of theflexible tube (See FIG. 14). In this regard, however, it goes withoutsaying that the available length is not limited to 1.6 m mentionedabove.

[0330] The details of each of the inner, outer and intermediate layersare as follows.

[0331] <Inner Layer>

[0332] The inner layer 31 was formed so as to have a single region witha uniform thickness. The thickness and a constituent material of theinner layer 31 were as follows.

[0333] Thickness: 0.2 mm

[0334] Material: A medium hardness polyurethane-based elastomer having ahardness of A81. (Hardness was measured in accordance with JIS K 7311.)

[0335] <Outer Layer>

[0336] The outer layer 32 was formed so as to have a single region witha uniform thickness. The thickness and a constituent material of theouter layer 32 were as follows.

[0337] Thickness: 0.1 mm

[0338] Material: A High hardness polyester-based elastomer having ahardness of A92 (Hardness was measured in accordance with JIS K 7311.)

[0339] <Intermediate Layer>

[0340] The intermediate layer 33 was formed so as to have a uniformthickness (0.3 mm) and to have first, second and third portions 33 a-33c. The first portion 33 a was formed at the tip side, the second portion33 b was formed between the first and third portions 33 a and 33 c, andthe third portion 33 c was formed at the base side. The first portion 33a was contiguous to the second portion 33 b through a boundary 34, andthe third portion 33 c was contiguous to the second portion 33 b througha boundary 34. The details of each of the portions 33 a-33 c are asfollows.

[0341] --First Portion--

[0342] Length: 440 mm

[0343] Material: A low hardness polyurethane-based elastomer having ahardness of A68. (Hardness was measured in accordance with JIS K 7311.)

[0344] --Second Portion--

[0345] Length: 530 mm

[0346] Material: A medium hardness polyurethane-based elastomer having ahardness of A82. (Hardness was measured in accordance with JIS K 7311.)

[0347] --Third Portion--

[0348] Length: 630 mm

[0349] Material: A high hardness polyurethane-based elastomer having ahardness of A90. (Hardness was measured in accordance with JIS K 7311.)

Example 3b

[0350] A flexible tube for an endoscope was prepared in the same manneras in Example 3a except that the configuration of an intermediate layer33 was changed as follows.

[0351] --First Portion--

[0352] Length: 450 mm

[0353] Material: A low hardness polyurethane-based elastomer having ahardness of A68. (Hardness was measured in accordance with JIS K 7311.)

[0354] --Second Portion--

[0355] Length: 300 mm

[0356] Material: A medium hardness polyurethane-based elastomer having ahardness of A82. (Hardness was measured in accordance with JIS K 7311.)

[0357] --Third Portion--

[0358] Length: 450 mm

[0359] Material: A high hardness polyurethane-based elastomer having ahardness of A90. (Hardness was measured in accordance with JIS K 7311.)

[0360] --Boundary Parts--

[0361] In this Example, two boundary parts 37 each of which had a lengthof 200 mm were formed in the intermediate layer 33. One of the boundarypart 37 was formed between the first and second portions 33 a and 33 b,and the other boundary part 37 was formed between the second and thirdportions 33 b and 33 c. Each of the boundary parts 37, was formedthrough an extrusion molding process so that its property graduallychanges in the longitudinal direction. Specifically, first, a mixture ofa constituent material for the first portion 33 a and a constituentmaterial for the second portion 33 b was fed in an extrusion moldingmachine while gradually changing the mixing rate of these materials.Further, a mixture of a constituent material for the second portion 33 band a constituent material for the third portion 33 c was fed in theextrusion molding machine while gradually changing the mixing rate ofthese materials.

Example 3c

[0362] A flexible tube for an endoscope was prepared in the same manneras in Example 3a except that the configuration of each of outer andintermediate layer 32 and 33 was changed as follows.

[0363] <Outer Layer>

[0364] In this Example, the outer layer 32 was formed so as to have auniform thickness (0.1 mm), and so as to have three portions (i.e.,first, second and third portions 32 a- 32 c) and two boundary parts(property-varying regions) 36. The details of each of the portions 32a-32 c and the boundary parts 36 are as follows.

[0365] --First Portion--

[0366] Length: 450 mm

[0367] Material: A low hardness polyolefine-based elastomer having ahardness of A76. (Hardness was measured in accordance with JIS-K 7311.)

[0368] --Second Portion--

[0369] Length: 300 mm

[0370] Material: A medium hardness polyolefine-based elastomer having ahardness of A85. (Hardness was measured in accordance with JIS K 7311.)

[0371] --Third Portion--

[0372] Length: 450 mm

[0373] Material: A high hardness polyolefine-based elastomer having ahardness of A95. (Hardness was measured in accordance with JIS K 7311.)

[0374] --Boundary Part-

[0375] In this Example, each of the boundary parts 36 had a length of200 mm. One of the boundary part 36 was formed between the first andsecond portions 32 a and 32 b, and the other boundary part 36 was formedbetween the second and third portions 32 b and 32 c.

[0376] <Intermediate Layer>

[0377] In this Example, the intermediate layer 33 was formed so as tohave a single region with a uniform thickness (0.3 mm). A constituentmaterial of the intermediate layer 33 was as follows.

[0378] Material: A low hardness polyurethane-based elastomer having ahardness of A78. (Hardness was measured in accordance with JIS K 7311.)

Example 3d

[0379] A flexible tube for an endoscope was prepared in the same manneras in Example 3c except that the configuration of an inner layer 31 ofan outer cover 3 was changed as follows.

[0380] In this Example, the inner layer 31 was formed so as to have auniform thickness (0.2 mm), and so as to have two portions (i.e., firstand second portions 31 a and 31 b) and a boundary part (property-varyingregion) 35. The details of each of the portions 31 a and 31 b and theboundary part 35 are as follows.

[0381] --First Portion--

[0382] Length: 600 mm

[0383] Material: A medium hardness polyurethane-based elastomer having ahardness of A82. (Hardness was measured in accordance with JIS K 7311.)

[0384] --Second Portion--

[0385] Length: 600 mm

[0386] Material: A high hardness polyurethane-based elastomer having ahardness of A91. (Hardness was measured in accordance with JIS K 7311.)

[0387] --Boundary Parts--

[0388] In this Example, the boundary part 35 having a length of 400 mmwas formed between the first and second portions 31 a and 31 b.

Comparative Example 3a

[0389] A core body 2 was prepared in the same manner as in Example 3a.Then, using an extrusion-molding machine, an outer cover 3 composed ofinner and outer layers 31 and 32 was provided on the outer periphery ofthe core body 2 so that the core body 2 was covered with the outer cover3. In this way, a flexible tube for an endoscope with a length of 1.6 mwas prepared. The details of each of the layers 31 and 32 of the outercover 3 are as follows.

[0390] <Inner Layer>

[0391] The inner layer 31 was formed so as to have a single region witha uniform thickness. The thickness and a constituent material of theinner layer 31 were as follows.

[0392] Thickness: 0.3 mm

[0393] Material: A medium hardness polyurethane-based elastomer having ahardness of A81. (Hardness was measured in accordance with JIS K 7311.)

[0394] <Outer Layer>

[0395] The outer layer 32 was formed so as to have a single region witha uniform thickness. The thickness and a constituent material of theouter layer 32 were as follows.

[0396] Thickness: 0.3 mm

[0397] Material: A low hardness polyurethane-based elastomer having ahardness of A68. (Hardness was measured in accordance with JIS K 7311.)

Comparative Example 3b

[0398] A flexible tube for an endoscope was prepared in the same manneras in Comparative Example 3a except that a constituent material for eachof inner and outer layers 31 and 32 was changed as follows.

[0399] <Inner Layer>

[0400] Material: A medium hardness polyurethane-based elastomer having ahardness of A81. (Hardness was measured in accordance with JIS K 7311.)

[0401] <Outer Layer>

[0402] Material: A high hardness polyester-based elastomer having ahardness of A92. (Hardness was measured in accordance with JIS K 7311.)

Comparative Example 3c

[0403] A flexible tube for an endoscope was prepared in the same manneras in Comparative Example 3a except that a constituent material for eachof inner and outer layers 31 and 32 was changed as follows.

[0404] <Inner Layer>

[0405] Material: A high hardness polyurethane-based elastomer having ahardness of A90. (Hardness was measured in accordance with JIS K 7311.)

[0406] <Outer Layer>

[0407] Material: A high hardness polyester-based elastomer having ahardness of A92. (Hardness was measured in accordance with JIS K 7311.)

[0408] 2. Observation of the Prepared Flexible Tubes

[0409] An observation of the cross-section of the outer cover wascarried out for each of the flexible tubes of Examples 3a-3d andComparative Examples 3a-3c. Through the observation, formation ofprojections 4 as shown in FIG. 2 was observed in each of the flexibletubes of Examples 3a-3d and Comparative Examples 3a and 3b, but noformation of projections 4 was observed in the flexible tube ofComparative Example 3c.

[0410] 3. Measurement of Rate of Change in Bending Stiffness

[0411] The rate of change in the bending stiffness in the longitudinaldirection was measured for each of the flexible tubes of Examples 3a-3d.

[0412] For each flexible tube, first the flexible tube was divided intonine sections (i.e., first-ninth sections as shown in FIG. 14) whichhave an equal length (177 mm) in the longitudinal direction, and thenthe bending stiffness in “each” of the nine sections of the flexibletube was measured according to the following method.

[0413] In the measurement, as shown in FIG. 15, first the flexible tubewas laid on two supporting-points located a distance L (177 mm) a partso that both ends of one of the sections were supported by the twosupporting-points. Then, the magnitude of the pressing force F when thecentral point of the section was displaced downward by a predetermineddistance y (50 mm) was measured and defined as the bending stiffness ofthe section. Based on the measured value, the rate of change in thebending stiffness in the longitudinal direction of the flexible tube wascalculated. The results of this measurement are shown in the attachedTable 5.

[0414] 4. Evaluation of Flexible Tube

[0415] (4-1) Insertion (Operationability) Test

[0416] An insertion test was carried out for each of the flexible tubesof Examples 3a-3d and Comparative Examples 3a-3c to evaluateoperationability of an endoscope with the flexible tube during insertionof the endoscope.

[0417] Before carrying out the insertion test, endoscopes as shown inFIG. 1 were prepared using the flexible tubes of Examples 3a-3d andComparative Examples 3a-3c. Further, a living body model having aninternal structure similar to an internal portion of a human body wasprepared. Then, each of the prepared endoscopes was inserted into theinternal portion of the living body model until its tip end (i.e., tipof an bendable tube 5) reaches a portion corresponding to a largeintestine of a human body. In the insertion test, the operationabilityduring insertion of the endoscope was evaluated in accordance with thefour rankings A-D given below.

[0418] Rank A:

[0419] It is possible to perform insertion operation very smoothly. (Aflexible tube of an endoscope of Rank A is considered to be best suitedfor use as a flexible tube for an endoscope.)

[0420] Rank B:

[0421] It is possible to perform insertion operation smoothly. (Aflexible tube of an endoscope of Rank B is considered to be suited foruse as a flexible tube for an endoscope.)

[0422] Rank C:

[0423] It takes a relatively long time to complete insertion operation.(A flexible tube of an endoscope of Rank C is considered to haveproblems for use as a flexible tube for an endoscope.)

[0424] Rank D:

[0425] It is difficult to complete insertion operation. (A flexible tubeof an endoscope of Rank D is considered to be unsuited for use as aflexible tube for an endoscope.)

[0426] The results of the insertion test are shown in the attached Table6.

[0427] (4-2) Chemical Resistance Test

[0428] A chemical resistance test was carried out for each of theflexible tubes of Example 3a-3d and Comparative Example 3a-3c. In thistest, 100L of 10% aqueous solution of iodine held at 25° C. was preparedfirst, and then each of the prepared flexible tubes was immersed in theaqueous solution for 200 hours. Then, the condition of each flexibletube was evaluated in accordance with the four rankings A-D given below.

[0429] Rank A:

[0430] No Change in the Appearance; and

[0431] No Occurrence of Cracks and Blisters in Outer Cover.

[0432] Rank B:

[0433] Slight Change in the Appearance; and

[0434] Occurrence of Blisters at a Few Spots of Outer Cover.

[0435] Rank C:

[0436] Large Change in the Appearance; and

[0437] Occurrence of Blisters at Many Spots of Outer Cover.

[0438] Rank D:

[0439] Extremely Large Change in the Appearance; and

[0440] Occurrence of a Large Number of Cracks and Blisters on OuterCover.

[0441] The evaluation result in this test is shown in the attached Table6.

[0442] (4-3) Durability Test

[0443] A durability test was carried out for each of the flexible tubesof Examples 3a-3d and Comparative Examples 3a-3c. In the durabilitytest, each of the flexible tubes was set to a state where the flexibletube was supported at its both ends, and in this state the operation ofbending by 90° was repeated 300 times. Then, the degree of change in theflexibility after the repeated operation of bending was examined toevaluate the durability of each flexible tube in accordance with thefour rankings A-D given below.

[0444] Rank A:

[0445] Almost No Change in Flexibility (A flexible tube of Rank A isconsidered to have extremely high durability.)

[0446] Rank B:

[0447] Slight Lowering of Flexibility (A flexible tube of Rank B isconsidered to have high durability.)

[0448] Rank C:

[0449] Large Lowering of Flexibility (A flexible tube of Rank C isconsidered to have problems in its durability.)

[0450] Rank D:

[0451] Extremely Large Lowering of Flexibility; and

[0452] Occurrence of cracks and the like at many spots of the outercover.

[0453] (A flexible tube of Rank D is considered to be unsuited for useas a flexible tube for an endoscope.)

[0454] The result of the durability test is shown in the attached Table6.

[0455] (4-4) Evaluation

[0456] The results in the attached Tables 5 and 6 show that the flexibletube according to the present invention (i.e., Examples 3a-3d) hasexcellent operationability and high chemical resistance as well as highdurability. Further, the results in Table 6 also show that conventionalflexible tubes (i.e., Comparative Examples 3a-3c) have some drawbacks.

[0457] Specifically, the flexible tube of Comparative Example 3a haspoor chemical resistance as well as poor operationability. The poorchemical resistance of this flexible tube is considered to result fromthe fact that the outer layer of the outer cover is made of the materialhaving poor resistance to chemical. Further, the flexible tube ofComparative Example 3b has poor operationability. Furthermore, theflexible tube of Comparative Example 3c has poor durability as well aspoor operationability. The poor durability of this flexible tube isconsidered to result from the fact that projections 4 as shown in FIG. 2have not been formed on the inner layer 31.

[0458] According to the present invention described above, appropriatematerials that are suitable for each of layers of an outer cover areused for preparing the outer cover, and the outer cover is provided ontothe core body so that each of the layers has appropriate thickness andshape. This structure and the selection of material make it possible toproduce a flexible tube for an endoscope that has high durability, highflexibility and high chemical resistance as well as excellentoperationability.

[0459] Further, according to the present invention, at least one oflayers of an outer cover 3 has at least two distinct portions and aboundary part along its longitudinal direction, and one of the portionsis contiguous to the other portion through the boundary part. In thislayer, one of the portions is different from the other portion adjacentthereto in physical property or chemical property. This configurationmakes it possible for a flexible tube to have a stiffness (flexibility)which gradually varies in its longitudinal direction.

[0460] According to an endoscope having the flexible tube as describedabove, since the flexible tube has a higher stiffness in a portioncloser to the base end, it is possible to fully transmit to the tip endof the endoscope the push-in force and the rotational force applied byan operator. On the other hand, since the flexible tube has a higherflexibility in a portion closer to the tip end, it is also possible tosmoothly insert an insertion section (flexible tube) of the endoscopeinto an internal curved portion of a patient in a safe manner.Therefore, the flexible tube as described above makes it possible for anoperator to insert the insertion section with easy manipulation, thusenabling the reduction of the burden on the patient during theendoscopic examination.

[0461] Furthermore, according to the present invention, a materialhaving high elasticity is used as a constituent material for anintermediate layer of the outer cover. This makes it possible to givehigh flexibility to a flexible tube.

[0462] Moreover, according to the present invention, a material havinghigh chemical resistance is used as a constituent material for an outerlayer of the outer cover. This makes it possible to give high chemicalresistance to a flexible tube.

[0463] In addition, according to the present invention, a materialhaving a high adhesion with a core body is used as a constituentmaterial for an inner layer of the outer cover. This makes it possibleto give high durability to a flexible tube.

[0464] Finally, it is to be understood that many changes and additionsmay be made to the embodiments described above without departing fromthe scope and spirit of the invention as defined in the appended Claims.

[0465] Further, it is also to be understood that the present disclosurerelates to subject matter contained in Japanese Patent Application Nos.2000-134922, 2000-142206 and 2000-156783 (filed on May 8, 15 and 26,2000, respectively) which are expressly incorporated herein by referencein its entirety. TABLE 1 Inner Layer Intermediate Layer Outer LayerThickness Thickness Thickness Chemical Material* [mm] Material* [mm]Material* [mm] Resistance Flexibility Durability Ex. 1a M 0.3 L 0.2 H10.1 A A A Ex. 1b M 0.2 L 0.2 H1 0.1 A A A Ex. 1c M 0.3 L 0.1 H1 0.1 A AA Ex. 1d M 0.3 L 0.2 H2 0.05 A A A Ex. 1e M 0.3 L 0.2 H3 0.1 A A A Co.Ex. 1a M 0.3 — — L 0.2 D C B Co. Ex. 1b M 0.3 — — H1 0.2 A D B Co. Ex.1c H1 0.2 — — M 0.3 C D D Co. Ex. 1d L 0.3 — — H1 0.2 A C D

[0466] TABLE 2 Intermediate Outer Inner Layer Layer Layer ExampleMaterial M Material L Material H1 2a Example Material M Material LMaterial H1 2b Example Material M Material L Material H1 2c ExampleMaterial M Material L Material H2 2d Example Material M Material LMaterial H3 2e Co. Example Material M — Material L 2a Co. ExampleMaterial M — Material H1 2b Co. Example Material H1 — Material H2 2c

[0467] TABLE 3 First Second Third Fourth Fifth Sixth Seventh EighthSection Section Section Section Section Section Section Section Example1 1.1 1.3 1.4 1.5 1.6 1.8 1.9 2a Example 1 1.2 1.4 1.6 1.8 1.9 2.1 2.32b Example 1 1 1.5 1.5 1.8 1.8 2.2 2.2 2c Example 1 1.3 1.5 1.7 1.9 2.12.3 2.4 2d Example 1 1.1 1.3 1.4 1.5 1.6 1.8 1.9 2e

[0468] TABLE 4 Chemical Operationability Resistance Durability Example AA A 2a Example A A A 2b Example A A A 2c Example A A A 2d Example A A A2e Co. Example C D B 2a Co. Example D A B 2b Co. Example D A D 2c

[0469] TABLE 5 First Second Third Fourth Fifth Sixth Seventh EighthNinth Section Section Section Section Section Section Section SectionSection Example 1 1.02 1.2 1.2 1.2 1.4 1.4 1.4 1.4 3a Example 1 1.041.11 1.2 1.2 1.3 1.38 1.39 1.4 3b Example 1 1.03 1.08 1.17 1.18 1.261.35 1.36 1.38 3c Example 1 1.06 1.12 1.19 1.27 1.34 1.38 1.4 1.42 3d

[0470] TABLE 6 Chemical Operationability Resistance Durability Example AA A 3a Example A A A 3b Example A A A 3c Example A A A 3d Co. Example CD B 3a Co. Example D A B 3b Co. Example D A D 3c

What is claimed is:
 1. A flexible tube for an endoscope, comprising: anelongated tubular core body; and an outer cover which is provided overthe core body, the outer cover having a portion which is formed into alaminate structure composed of at least three layers, the layers of thelaminate structure including an inner layer, an outer layer and at leastone intermediate layer formed between the inner layer and the outerlayer, wherein the intermediate layer of the outer cover has a higherelasticity than the inner and outer layers so that the intermediatelayer functions as cushioning between the inner layer and the outerlayer, wherein at least one of the layers constituting the portion ofthe laminate structure has a thickness-varying region where thethickness of the layer varies in its longitudinal direction.
 2. Theflexible tube as claimed in claim 1, wherein the thickness-varyingregion extends substantially over an entire region of the layer, andwithin the thickness-varying region the thickness of the layer varies inits longitudinal direction in a gradual or stepwise manner.
 3. Theflexible tube as claimed in claim 1, wherein the layer with thethickness-varying region has at least one uniform thickness region whichis formed so as to adjoin the thickness-varying region.
 4. The flexibletube as claimed in claim 1, wherein the layer having thethickness-varying region is formed of a material that is different frommaterials constituting the other layers in its hardness.
 5. The flexibletube as claimed in claim 1, wherein each of at least two of the layersconstituting the portion of the laminate structure has athickness-varying region where the thickness of the layer varies in itslongitudinal direction.
 6. The flexible tube as claimed in claim 1,wherein the outer cover is provided over the core body through anextrusion molding process.
 7. The flexible tube as claimed in claim 6,wherein in the extrusion molding process a constituent material for eachof the layers is fed at a predetermined feeding rate while the core bodyis fed at a predetermined feeding speed, in which the thickness of thelayer having the thickness-varying region is controlled by adjusting thefeeding rate of the material for the layer during the extrusion moldingprocess and/or adjusting the feeding speed of the core body during theextrusion molding process.
 8. A flexible tube for an endoscope,comprising: an elongated tubular core body; and an outer cover which isprovided over the core body, the outer cover having a portion which isformed into a laminate structure composed of at least three layers, thelayers of the laminate structure including an inner layer, an outerlayer and at least one intermediate layer formed between the inner layerand the outer layer, wherein the intermediate layer of the outer coverhas a higher elasticity than the inner and outer layers so that theintermediate layer functions as cushioning between the inner layer andthe outer layer, wherein at least one of the layers constituting theportion of the laminate structure has a thickness-varying region wherethe thickness of the layer varies in its longitudinal direction, whereinat least one of the layers constituting the portion of the laminatestructure has at least two regions and at least one boundary part alongits longitudinal direction, and one of the regions is contiguous to theother region through the boundary part, in which one of the regions isdifferent from the other regions adjacent thereto in its physicalproperty and/or chemical property.
 9. The flexible tube as claimed inclaim 8, wherein one of the regions is formed of a material which isdifferent from that forming the other region adjacent thereto.
 10. Theflexible tube as claimed in claim 8, wherein each of at least two of thelayers constituting the portion of the laminate structure has at leasttwo regions and at least one boundary part along its longitudinaldirection, and one of the regions is contiguous to the other regionthrough the boundary part, in which one of the regions is different fromthe other region adjacent thereto in its physical property and/orchemical property.
 11. The flexible tube as claimed in claim 10, whereinthe outer cover is formed such that the boundary part of one layer isnot located above or below the boundary part of the other layer in itsthickness direction.
 12. The flexible tube as claimed in claim 8,wherein the boundary part is formed as a property-varying part withinwhich the physical property and/or the chemical property of the layergradually vary in its longitudinal direction.
 13. The flexible tube asclaimed in claim 12, wherein the boundary part is formed of a mixture ofa material constituting one of the regions and a material constitutingthe other region.
 14. The flexible tube as claimed in claim 8, whereinthe layer having the boundary part is formed such that the physicalproperty and/or the chemical property within the boundary part vary inits longitudinal direction in a substantially stepwise manner.
 15. Theflexible tube as claimed in claim 8, wherein in the layer having the atleast two regions, one of the regions is different from the other regionadjacent thereto in its hardness.
 16. The flexible tube as claimed inclaim 8, wherein the flexible tube has tip and base ends, andflexibility of the flexible tube increases in a gradual or stepwisemanner along the direction from the base end to the tip end.